Beta-amino heterocyclic dipeptidyl peptidase inhibitors for the treatment or prevention of diabetes

ABSTRACT

The present invention is directed to compounds which are inhibitors of the dipeptidyl peptidase-IV enzyme (“DP-IV inhibitors”) and which are useful in the treatment or prevention of diseases in which the dipeptidyl peptidase-IV enzyme is involved, such as diabetes and particularly type 2 diabetes. The invention is also directed to pharmaceutical compositions comprising these compounds and the use of these compounds and compositions in the prevention or treatment of such diseases in which the dipeptidyl peptidase-IV enzyme is involved.

BACKGROUND OF THE INVENTION

Diabetes refers to a disease process derived from multiple causativefactors and characterized by elevated levels of plasma glucose orhyperglycemia in the fasting state or after administration of glucoseduring an oral glucose tolerance test. Persistent or uncontrolledhyperglycemia is associated with increased and premature morbidity andmortality. Often abnormal glucose homeostasis is associated bothdirectly and indirectly with alterations of the lipid, lipoprotein andapolipoprotein metabolism and other metabolic and hemodynamic disease.Therefore patients with Type 2 diabetes mellitus are at especiallyincreased risk of macrovascular and microvascular complications,including coronary heart disease, stroke, peripheral vascular disease,hypertension, nephropathy, neuropathy, and retinopathy. Therefore,therapeutical control of glucose homeostasis, lipid metabolism andhypertension are critically important in the clinical management andtreatment of diabetes mellitus.

There are two generally recognized forms of diabetes. In type 1diabetes, or insulin-dependent diabetes mellitus (IDDM), patientsproduce little or no insulin, the hormone which regulates glucoseutilization. In type 2 diabetes, or noninsulin dependent diabetesmellitus (NIDDM), patients often have plasma insulin levels that are thesame or even elevated compared to nondiabetic subjects; however, thesepatients have developed a resistance to the insulin stimulating effecton glucose and lipid metabolism in the main insulin-sensitive tissues,which are muscle, liver and adipose tissues, and the plasma insulinlevels, while elevated, are insufficient to overcome the pronouncedinsulin resistance.

Insulin resistance is not primarily due to a diminished number ofinsulin receptors but to a post-insulin receptor binding defect that isnot yet understood. This resistance to insulin responsiveness results ininsufficient insulin activation of glucose uptake, oxidation and storagein muscle and inadequate insulin repression of lipolysis in adiposetissue and of glucose production and secretion in the liver.

The available treatments for type 2 diabetes, which have not changedsubstantially in many years, have recognized limitations. While physicalexercise and reductions in dietary intake of calories will dramaticallyimprove the diabetic condition, compliance with this treatment is verypoor because of well-entrenched sedentary lifestyles and excess foodconsumption, especially of foods containing high amounts of saturatedfat. Increasing the plasma level of insulin by administration ofsulfonylureas (e.g. tolbutamide and glipizide) or meglitinide, whichstimulate the pancreatic β-cells to secrete more insulin, and/or byinjection of insulin when sulfonylureas or meglitinide becomeineffective, can result in insulin concentrations high enough tostimulate the very insulin-resistant tissues. However, dangerously lowlevels of plasma glucose can result from administration of insulin orinsulin secretagogues (sulfonylureas or meglitinide), and an increasedlevel of insulin resistance due to the even higher plasma insulin levelscan occur. The biguanides increase insulin sensitivity resulting in somecorrection of hyperglycemia. However, the two biguanides, phenformin andmetformin, can induce lactic acidosis and nausea/diarrhea. Metformin hasfewer side effects than phenformin and is often prescribed for thetreatment of Type 2 diabetes.

The glitazones (i.e. 5-benzylthiazolidine-2,4-diones) are a morerecently described class of compounds with potential for amelioratingmany symptoms of type 2 diabetes. These agents substantially increaseinsulin sensitivity in muscle, liver and adipose tissue in severalanimal models of type 2 diabetes resulting in partial or completecorrection of the elevated plasma levels of glucose without occurrenceof hypoglycemia. The glitazones that are currently marketed are agonistsof the peroxisome proliferator activated receptor (PPAR), primarily thePPAR-gamma subtype. PPAR-gamma agonism is generally believed to beresponsible for the improved insulin sensititization that is observedwith the glitazones. Newer PPAR agonists that are being tested fortreatment of Type II diabetes are agonists of the alpha, gamma or deltasubtype, or a combination of these, and in many cases are chemicallydifferent from the glitazones (i.e., they are not thiazolidinediones).Serious side effects (e.g. liver toxicity) have occurred with some ofthe glitazones, such as troglitazone.

Additional methods of treating the disease are still underinvestigation. New biochemical approaches that have been recentlyintroduced or are still under development include treatment withalpha-glucosidase inhibitors (e.g. acarbose) and protein tyrosinephosphatase-1B (PTP-1B) inhibitors.

Compounds that are inhibitors of the dipeptidyl peptidase-IV (“DP-IV” or“DPP-IV”) enzyme are also under investigation as drugs that may beuseful in the treatment of diabetes, and particularly type 2 diabetes.See for example WO 97/40832, WO 98/19998, U.S. Pat. No. 5,939,560,Bioorg. Med. Chem. Lett., 6: 1163-1166 (1996); and Bioorg. Med. Chem.Lett., 6: 2745-2748 (1996). The usefulness of DP-IV inhibitors in thetreatment of type 2 diabetes is based on the fact that DP-IV in vivoreadily inactivates glucagon like peptide-1 (GLP-1) and gastricinhibitory peptide (GIP). GLP-1 and GIP are incretins and are producedwhen food is consumed. The incretins stimulate production of insulin.Inhibition of DP-IV leads to decreased inactivation of the incretins,and this in turn results in increased effectiveness of the incretins instimulating production of insulin by the pancreas. DP-IV inhibitiontherefore results in an increased level of serum insulin.Advantageously, since the incretins are produced by the body only whenfood is consumed, DP-IV inhibition is not expected to increase the levelof insulin at inappropriate times, such as between meals, which can leadto excessively low blood sugar (hypoglycemia). Inhibition of DP-IV istherefore expected to increase insulin without increasing the risk ofhypoglycemia, which is a dangerous side effect associated with the useof insulin secretagogues.

DP-UV inhibitors also have other therapeutic utilities, as discussedherein. DP-IV inhibitors have not been studied extensively to date,especially for utilities other than diabetes. New compounds are neededso that improved DP-IV inhibitors can be found for the treatment ofdiabetes and potentially other diseases and conditions. The therapeuticpotential of DP-IV inhibitors for the treatment of type 2 diabetes isdiscussed by D. J. Drucker in Exp. Opin. Invest. Drugs, 12: 87-100(2003) and by K. Augustyns, et al., in Exp. Opin. Ther. Patents, 13:499-510 (2003).

SUMMARY OF THE INVENTION

The present invention is directed to compounds which are inhibitors ofthe dipeptidyl peptidase-IV enzyme (“DP-IV inhibitors”) and which areuseful in the treatment or prevention of diseases in which thedipeptidyl peptidase-IV enzyme is involved, such as diabetes andparticularly type 2 diabetes. The invention is also directed topharmaceutical compositions comprising these compounds and the use ofthese compounds and compositions in the prevention or treatment of suchdiseases in which the dipeptidyl peptidase-IV enzyme is involved.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to heterocyclic compounds useful asinhibitors of dipeptidyl peptidase-IV. Compounds of the presentinvention are described by structural formula I:

or a pharmaceutically acceptable salt thereof; wherein

-   each n is independently 0, 1, or 2;-   X is N or CR²⁻;-   Ar is phenyl substituted with one to five R³ substituents;-   R¹ and R² are each independently selected from the group consisting    of    -   hydrogen,    -   halogen,    -   cyano,    -   C₁₋₁₀ alkyl, wherein alkyl is unsubstituted or substituted with        one to five halogens,    -   C₁₋₁₀ alkoxy, wherein alkoxy is unsubstituted or substituted        with one to five substituents independently selected from        halogen or hydroxy,    -   C₁₋₁₀ alkylthio, wherein alkylthio is unsubstituted or        substituted with one to five substituents independently selected        from halogen or hydroxy,    -   C₂₋₁₀ alkenyl, wherein alkenyl is unsubstituted or substituted        with one to five substituents independently selected from        halogen or hydroxy,    -   (CH₂)_(n)COOH,    -   (CH₂)_(n)COOC₁₋₆ alkyl,    -   (CH₂)_(n)CONR⁴R⁵, wherein R⁴ and R⁵ are independently selected        from the group consisting of hydrogen, tetrazolyl, thiazolyl,        (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆ cycloalkyl, and C₁₋₆ alkyl,        wherein alkyl is unsubstituted or substituted with one to five        halogens and wherein phenyl and cycloalkyl are unsubstituted or        substituted with one to five substituents independently selected        from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein        alkyl and alkoxy are unsubstituted or substituted with one to        five halogens;    -   or R⁴ and R⁵ together with the nitrogen atom to which they are        attached form a heterocyclic ring selected from azetidine,        pyrrolidine, piperidine, piperazine, and morpholine wherein said        heterocyclic ring is unsubstituted or substituted with one to        five substituents independently selected from halogen, hydroxy,        C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxy are        unsubstituted or substituted with one to five halogens;    -   (CH₂)_(n)—NR⁴R⁵,    -   (CH₂)_(n)—OCONR⁴R⁵,    -   (CH₂)_(n)—SO₂NR⁴R⁵,    -   (CH₂)_(n)—SO₂R⁶,    -   (CH₂)_(n)—NR⁷SO₂R⁶,    -   (CH₂)_(n)—NR⁷CONR⁴R⁵,    -   (CH₂)_(n)—NR⁷COR⁷,    -   (CH₂)_(n)—NR⁷CO₂R⁶,    -   (CH₂)_(n)—COR⁶,    -   (CH₂)_(n)-aryl, wherein aryl is unsubstituted or substituted        with one to five substituents independently selected from        halogen, CN, hydroxy, NR⁷SO₂R⁶, SO₂R⁶, CO₂H, C₁₋₆        alkyloxycarbonyl, C₁₋₆ alkyl and C₁₋₆ alkoxy, wherein alkyl and        alkoxy are unsubstituted or substituted with one to five        substituents independently selected from halogen, CO₂H, and C₁₋₆        alkyloxycarbonyl,    -   (CH₂)_(n)-heteroaryl, wherein heteroaryl is unsubstituted or        substituted with one to three substituents independently        selected from hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are unsubstituted or substituted with        one to five halogens,    -   (CH₂)_(n)-heterocyclyl, wherein heterocyclyl is unsubstituted or        substituted with one to three substituents independently        selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆        alkoxy, wherein alkyl and alkoxy are unsubstituted or        substituted with one to five halogens,    -   (CH₂)_(n)—C₃₋₆ cycloalkyl, wherein cycloalkyl is unsubstituted        or substituted with one to three substituents independently        selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are unsubstituted or substituted with        one to five halogens; and    -   wherein any methylene (CH₂) carbon atom in R¹ or R² is        unsubstituted or substituted with one to two groups        independently selected from halogen, hydroxy, and C₁₋₄ alkyl        unsubstituted or substituted with one to five halogens;-   each R³ is independently selected from the group consisting of    -   hydrogen,    -   halogen,    -   cyano,    -   hydroxy,    -   C₁₋₆ alkyl, unsubstituted or substituted with one to five        halogens, and    -   C₁₋₆ alkoxy, unsubstituted or substituted with one to five        halogens;-   R⁶ is independently selected from the group consisting of    tetrazolyl, thiazolyl, (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆ cycloalkyl,    and C₁₋₆ alkyl, wherein alkyl is unsubstituted or substituted with    one to five halogens and wherein phenyl and cycloalkyl are    unsubstituted or substituted with one to five substituents    independently selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆    alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted    with one to five halogens, and wherein any methylene (CH₂) carbon    atom in R⁶ is unsubstituted or substituted with one to two groups    independently selected from halogen, hydroxy, C₁₋₄ alkyl, and C₁₋₄    alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted    with one to five halogens;-   each R⁷ is hydrogen or R⁶;-   R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are each independently selected from    the group consisting of:    -   hydrogen,    -   cyano,    -   (CH₂)_(n)COOH,    -   (CH₂)_(n)COOC₁₋₆ alkyl, wherein alkyl is unsubstituted or        substituted with one to three substituents independently        selected from halogen and phenyl,    -   C₁₋₁₀ alkyl, unsubstituted or substituted with one to five        substituents independently selected from halogen, hydroxy, C₁₋₆        alkoxy, carboxy, C₁₋₆ alkyloxycarbonyl, and phenyl-C₁₋₃ alkoxy,        wherein alkoxy is unsubstituted or substituted with one to five        halogens,    -   (CH₂)_(n)-aryl, wherein aryl is unsubstituted or substituted        with one to five substituents independently selected from        halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and        alkoxy are unsubstituted or substituted with one to five        halogens,    -   (CH₂)_(n)-heteroaryl, wherein heteroaryl is unsubstituted or        substituted with one to three substituents independently        selected from hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are unsubstituted or substituted with        one to five halogens,    -   (CH₂)_(n)-heterocyclyl, wherein heterocyclyl is unsubstituted or        substituted with one to three substituents independently        selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆        alkoxy, wherein alkyl and alkoxy are unsubstituted or        substituted with one to five halogens,    -   (CH₂)_(n)—C₃₋₆ cycloalkyl, wherein cycloalkyl is unsubstituted        or substituted with one to three substituents independently        selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are unsubstituted or substituted with        one to five halogens,    -   (CH₂)_(n)CONR⁴R⁵, wherein R⁴ and R⁵ are independently selected        from the group consisting of hydrogen, tetrazolyl, thiazolyl,        (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆ cycloalkyl, and C₁₋₆ alkyl,        wherein alkyl is unsubstituted or substituted with one to five        halogens and wherein phenyl and cycloalkyl are unsubstituted or        substituted with one to five substituents independently selected        from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein        alkyl and alkoxy are unsubstituted or substituted with one to        five halogens;        -   or wherein R⁴ and R⁵ together with the nitrogen atom to            which they are attached form a heterocyclic ring selected            from azetidine, pyrrolidine, piperidine, piperazine and            morpholine wherein said heterocyclic ring is unsubstituted            or substituted with one to five substituents independently            selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy,            wherein alkyl and alkoxy are unsubstituted or substituted            with one to five halogens; and    -   wherein any methylene (CH₂) carbon atom in R⁸, R⁹, R¹⁰, R¹¹,        R¹², or R¹³ is unsubstituted or substituted with one to two        groups independently selected from halogen, hydroxy, and C₁₋₄        alkyl unsubstituted or substituted with one to five halogens.

In one embodiment of the compounds of the present invention, the carbonatom marked with an * has the R configuration as depicted in formula Ia

wherein Ar, X, R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹² and R¹³ are as defined herein.

In a second embodiment of the compounds of the present invention, X is Nas depicted in formula Ib:

wherein Ar, R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined herein.

In a class of this second embodiment, the carbon atom marked with an *has the R configuration as depicted in formula Ic:

wherein Ar, R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined herein.

In another class of this second embodiment of the compounds of thepresent invention, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are hydrogen as depictedin formula Id:

wherein Ar, R¹, and R⁸ are as defined herein.

In a third embodiment of the compounds of the present invention, X isCR² as depicted in formula Ie:

wherein Ar, R¹, R², R⁸, R⁹, R¹⁰, R¹, R¹², and R¹³ are as defined herein.

In a class of this third embodiment, the carbon atom marked with an *has the R configuration as depicted in formula If:

wherein Ar, R¹, R², R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as definedherein.

In another class of this third embodiment of the compounds of thepresent invention, R⁹, R¹⁰, R¹¹, R¹² and R¹³ are hydrogen as depicted informula Ig:

wherein Ar, R¹, R², and R⁸ are as defined herein.

In a fourth embodiment of the compounds of the present invention, R³ isselected from the group consisting of hydrogen, fluoro, chloro, bromo,trifluoromethyl, and methyl. In a class of this embodiment, R³ isselected from the group consisting of hydrogen, fluoro, and chloro. In asubclass of this class, R³ is hydrogen or fluoro.

In a fifth embodiment of the compounds of the present invention, R¹ isselected from the group consisting of:

-   -   hydrogen,    -   C₁₋₆ alkyl, wherein alkyl is unsubstituted or substituted with        one to five fluorines,    -   (CH₂)_(n)-phenyl wherein phenyl is unsubstituted or substituted        with one to five substituents independently selected from        hydroxy, halogen, C₁₋₆ alkyl, C₁₋₆ alkoxy, wherein alkyl and        alkoxy are unsubstituted or substituted with one to five        halogens,    -   C₃₋₆ cycloalkyl, unsubstituted or substituted with one to five        substituents independently selected from halogen, hydroxy, C₁₋₆        alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxy are        unsubstituted or substituted with one to five halogens; and    -   wherein any methylene (CH₂) carbon atom in R¹ is unsubstituted        or substituted with one to two groups independently selected        from halogen, hydroxy, and C₁₋₄ alkyl unsubstituted or        substituted with one to five halogens.

In a class of this embodiment of the compounds of the present invention,R¹ is selected from the group consisting of

-   -   hydrogen,    -   methyl,    -   ethyl,    -   difluoromethyl,    -   trifluoromethyl,    -   CH₂CF₃,    -   CF₂CF₃,    -   phenyl, and    -   cyclopropyl.

In a subclass of this class, R¹ is selected from the group consisting ofhydrogen, difluoromethyl, trifluoromethyl, phenyl, and cyclopropyl.

In a sixth embodiment of the compounds of the present invention, R² isselected from the group consisting of hydrogen,

-   -   C₁₋₆ alkyl, unsubstituted or substituted with one to five        fluorines, phenyl, unsubstituted or substituted with one to        three substituents independently selected from fluoro, chloro,        trifluoromethyl, methoxy, and OCF₃, and    -   C₃₋₆ cycloalkyl, unsubstituted or substituted with one to five        substituents independently selected from halogen, hydroxy, C₁₋₆        alkyl, and    -   C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted or        substituted with one to five halogens.

In a class of this embodiment of the compounds of the present invention,R² is selected from the group consisting of hydrogen, trifluoromethyl,phenyl, and cyclopropyl. In a subclass of this class, R² is hydrogen ortrifluoromethyl.

In a seventh embodiment of the compounds of the present invention, R¹¹,R¹², and R¹³ are each hydrogen and R⁸, R⁹, and R¹⁰ are eachindependently selected from the group consisting of:

-   -   hydrogen,    -   C₁₋₆ alkyl, unsubstituted or substituted with one to five        substituents independently selected from halogen, hydroxy, C₁₋₆        alkoxy, and phenyl-C₁₋₃ alkoxy, wherein alkoxy is unsubstituted        or substituted with one to five halogens,    -   (CH₂)_(n)COOH,    -   (CH₂)_(n)COOC₁₋₆ alkyl, wherein alkyl is unsubstituted or        substituted with one to three substituents independently        selected from halogen and phenyl,    -   (CH₂)_(n)CONR⁴R⁵, wherein R⁴ and R⁵ are independently selected        from the group consisting of hydrogen, tetrazolyl, thiazolyl,        (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆ cycloalkyl, and C₁₋₆ alkyl,        wherein alkyl is unsubstituted or substituted with one to five        halogens and wherein phenyl and cycloalkyl are unsubstituted or        substituted with one to five substituents independently selected        from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein        alkyl and alkoxy are unsubstituted or substituted with one to        five halogens;        -   or wherein R⁴ and R⁵ together with the nitrogen atom to            which they are attached form a heterocyclic ring selected            from azetidine, pyrrolidine, piperidine, piperazine and            morpholine wherein said heterocyclic ring is unsubstituted            or substituted with one to five substituents independently            selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy,            wherein alkyl and alkoxy are unsubstituted or substituted            with one to five halogens,    -   (CH₂)_(n)-phenyl, wherein phenyl is unsubstituted or substituted        with one to five substituents independently selected from        halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and        alkoxy are unsubstituted or substituted with one to five        halogens,    -   (CH₂)_(n)-heteroaryl, wherein heteroaryl is unsubstituted or        substituted with one to three substituents independently        selected from hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are unsubstituted or substituted with        one to five halogens,    -   (CH₂)_(n)-heterocyclyl, wherein heterocyclyl is unsubstituted or        substituted with one to three substituents independently        selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆        alkoxy, wherein alkyl and alkoxy are unsubstituted or        substituted with one to five halogens,    -   (CH₂)_(n)—C₃₋₆ cycloalkyl, wherein cycloalkyl is unsubstituted        or substituted with one to three substituents independently        selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are optionally substituted with one to        five halogens; and    -   wherein any methylene (CH₂) carbon atom in R⁸, R⁹ or R¹⁰ is        unsubstituted or substituted with one to two groups        independently selected from halogen, hydroxy, and C₁₋₄ alkyl        unsubstituted or substituted with one to five halogens.

In a class of this embodiment of the compounds of the present invention,R⁸, R⁹, and R¹⁰ are each independently selected from the groupconsisting of:

-   -   hydrogen,    -   C₁₋₃ alkyl, unsubstituted or substituted with one to three        substituents independently selected from halogen, hydroxy, C₁₋₆        alkoxy, and phenyl-C₁₋₁₃ alkoxy, wherein alkoxy is unsubstituted        or substituted with one to five halogens,    -   (CH₂)_(n)COOH,    -   (CH₂)_(n)COOC₁₋₆ alkyl, wherein alkyl is unsubstituted or        phenyl,    -   (CH₂)_(n)CONR⁴R⁵, wherein R⁴ and R⁵ are independently selected        from the group consisting of hydrogen and C₁₋₆ alkyl, wherein        alkyl is unsubstituted or substituted with one to five halogens;        -   or wherein R⁴ and R⁵ together with the nitrogen atom to            which they are attached form a heterocyclic ring selected            from azetidine, pyrrolidine, piperidine, piperazine and            morpholine wherein said heterocyclic ring is unsubstituted            or substituted with one to five substituents independently            selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy,            wherein alkyl and alkoxy are unsubstituted or substituted            with one to five halogens,    -   (CH₂)_(n)-phenyl, wherein phenyl is unsubstituted or substituted        with one to five substituents independently selected from        halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and        alkoxy are unsubstituted or substituted with one to five        halogens,    -   (CH₂)_(n)-heteroaryl, wherein heteroaryl is unsubstituted or        substituted with one to three substituents independently        selected from hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆ alkoxy,        wherein alkyl and alkoxy are optionally substituted with one to        five halogens,    -   (CH₂)_(n)-heterocyclyl, wherein heterocyclyl is unsubstituted or        substituted with one to three substituents independently        selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆        alkoxy, wherein alkyl and alkoxy are optionally substituted with        one to five halogens,    -   (CH₂)_(n)—C₃₋₆ cyclopropyl; and    -   wherein any methylene (CH₂) carbon atom in R⁸, R⁹ or R¹⁰ is        unsubstituted or substituted with one to two groups        independently selected from halogen, hydroxy, and C₁₋₄ alkyl        unsubstituted or substituted with one to five halogens.

In a subclass of this class, R⁸, R⁹, and R¹⁰ are each independentlyselected from the group consisting of:

-   -   hydrogen,    -   CH₃,    -   CH₂CH₃,    -   CH₂-cyclopropyl,    -   CHF-cyclopropyl,    -   CH(OH)-cyclopropyl,    -   CH₂OCH₂Ph,    -   CH₂(4-F-Ph),    -   CH₂(4-CF₃-Ph),    -   CH₂-[1,2,4]triazol-4-yl,    -   CH₂-(imidazol-1-yl),    -   CH₂-(pyrazol-1-yl),    -   CH₂—COOCH₂Ph,    -   CH₂—COOH,    -   CH₂—CONMe2, and    -   CH₂OCH₃.

In a further subclass of this class, R⁹ and R¹⁰ are each independentlyhydrogen or methyl.

As used herein the following definitions are applicable.

“Alkyl”, as well as other groups having the prefix “alk”, such as alkoxyand alkanoyl, means carbon chains which may be linear or branched, andcombinations thereof, unless the carbon chain is defined otherwise.Examples of alkyl groups include methyl, ethyl, propyl, isopropyl,butyl, sec- and tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, and thelike. Where the specified number of carbon atoms permits, e.g., fromC₃₋₁₀, the term alkyl also includes cycloalkyl groups, and combinationsof linear or branched alkyl chains combined with cycloalkyl structures.When no number of carbon atoms is specified, C₁₋₆ is intended.

“Cycloalkyl” is a subset of alkyl and means a saturated carbocyclic ringhaving a specified number of carbon atoms. Examples of cycloalkylinclude cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,cyclooctyl, and the like. A cycloalkyl group generally is monocyclicunless stated otherwise. Cycloalkyl groups are saturated unlessotherwise defined.

The term “alkoxy” refers to straight or branched chain alkoxides of thenumber of carbon atoms specified (e.g., C₁₋₆ alkoxy), or any numberwithin this range [i.e., methoxy (MeO—), ethoxy, isopropoxy, etc.].

The term “alkylthio” refers to straight or branched chain alkylsulfidesof the number of carbon atoms specified (e.g., C₁₋₆ alkylthio), or anynumber within this range [i.e., methylthio (MeS—), ethylthio,isopropylthio, etc.].

The term “alkylamino” refers to straight or branched alkylamines of thenumber of carbon atoms specified (e.g., C₁₋₆ alkylamino), or any numberwithin this range [i.e., methylamino, ethylamino, isopropylamino,t-butylamino, etc.].

The term “alkylsulfonyl” refers to straight or branched chainalkylsulfones of the number of carbon atoms specified (e.g., C₁₋₆alkylsulfonyl), or any number within this range [i.e., methylsulfonyl(MeSO₂—), ethylsulfonyl, isopropylsulfonyl, etc.].

The term “alkyloxycarbonyl” refers to straight or branched chain estersof a carboxylic acid derivative of the present invention of the numberof carbon atoms specified (e.g., C₁₋₆ alkyloxycarbonyl), or any numberwithin this range [i.e., methyloxycarbonyl (MeOCO—), ethyloxycarbonyl,or butyloxycarbonyl].

“Aryl” means a mono- or polycyclic aromatic ring system containingcarbon ring atoms. The preferred aryls are monocyclic or bicyclic 6-10membered aromatic ring systems. Phenyl and naphthyl are preferred aryls.The most preferred aryl is phenyl.

“Heterocycle” and “heterocyclyl” refer to saturated or unsaturatednon-aromatic rings or ring systems containing at least one heteroatomselected from O, S and N, further including the oxidized forms ofsulfur, namely SO and SO₂. Examples of heterocycles includetetrahydrofuran (THF), dihydrofuran, 1,4-dioxane, morpholine,1,4-dithiane, piperazine, piperidine, 1,3-dioxolane, imidazolidine,imidazoline, pyrroline, pyrrolidine, tetrahydropyran, dihydropyran,oxathiolane, dithiolane, 1,3-dioxane, 1,3-dithiane, oxathiane,thiomorpholine, and the like.

“Heteroaryl” means an aromatic or partially aromatic heterocycle thatcontains at least one ring heteroatom selected from O, S and N.“Heteroaryl” also includes heteroaryls fused to other kinds of rings,such as aryls, cycloalkyls and heterocycles that are not aromatic.Examples of heteroaryl groups include: pyrrolyl, isoxazolyl,isothiazolyl, pyrazolyl, pyridyl, oxazolyl, oxadiazolyl, thiadiazolyl,thiazolyl, imidazolyl, triazolyl, tetrazolyl, furyl, triazinyl, thienyl,pyrimidyl, pyrazinyl, benzisoxazolyl, benzoxazolyl, benzothiazolyl,benzothiadiazolyl, dihydrobenzofuranyl, indolinyl, pyridazinyl,indazolyl, isoindolyl, dihydrobenzothienyl, indolizinyl, cinnolinyl,phthalazinyl, quinazolinyl, naphthyridinyl, carbazolyl, benzodioxolyl,quinoxalinyl, purinyl, furazanyl, isobenzylfuranyl, benzimidazolyl,benzofuranyl, benzothienyl, quinolyl, indolyl, isoquinolyl,dibenzofuranyl,imidazo[1,2-α]pyridinyl,[1,2,4-triazolo][4,3-α]pyridinyl,pyrazolo[1,5-α]pyridinyl, [1,2,4-triazolo][1,5-α]pyridinyl,2-oxo-1,3-benzoxazolyl, 4-oxo-3H-quinazolinyl,3-oxo-[1,2,4]-triazolo[4,3-α]-2H-pyridinyl,5-oxo-[1,2,4]-4H-oxadiazolyl, 2-oxo-[1,3,4]-3H-oxadiazolyl,2-oxo-1,3-dihydro-2H-imidazolyl, 3-oxo-2,4-dihydro-3H-1,2,4-triazolyl,and the like. For heterocyclyl and heteroaryl groups, rings and ringsystems containing from 3-15 atoms are included, forming 1-3 rings.

“Halogen” refers to fluorine, chlorine, bromine and iodine. Chlorine andfluorine are generally preferred. Fluorine is most preferred when thehalogens are substituted on an alkyl or alkoxy group (e.g. CF₃O andCF₃CH₂O).

The compounds of the present invention may contain one or moreasymmetric centers and can thus occur as racemates and racemic mixtures,single enantiomers, diastereomeric mixtures and individualdiastereomers. The compounds of the present invention have oneasymmetric center at the carbon atom marked with an * in formula Ia.Additional asymmetric centers may be present depending upon the natureof the various substituents on the molecule. Each such asymmetric centerwill independently produce two optical isomers and it is intended thatall of the possible optical isomers and diastereomers in mixtures and aspure or partially purified compounds are included within the ambit ofthis invention. The present invention is meant to comprehend all suchisomeric forms of these compounds.

Some of the compounds described herein contain olefinic double bonds,and unless specified otherwise, are meant to include both E and Zgeometric isomers.

Some of the compounds described herein may exist as tautomers, whichhave different points of attachment of hydrogen accompanied by one ormore double bond shifts. For example, a ketone and its enol form areketo-enol tautomers. The individual tautomers as well as mixturesthereof are encompassed with compounds of the present invention.

Formula I shows the structure of the class of compounds withoutpreferred stereochemistry. Formula Ia shows the preferred sterochemistryat the carbon atom to which is attached the amino group of the betaamino acid from which these compounds are prepared.

The independent syntheses of these diastereomers or theirchromatographic separations may be achieved as known in the art byappropriate modification of the methodology disclosed herein. Theirabsolute stereochemistry may be determined by the x-ray crystallographyof crystalline products or crystalline intermediates which arederivatized, if necessary, with a reagent containing an asymmetriccenter of known absolute configuration.

If desired, racemic mixtures of the compounds may be separated so thatthe individual enantiomers are isolated. The separation can be carriedout by methods well known in the art, such as the coupling of a racemicmixture of compounds to an enantiomerically pure compound to form adiastereomeric mixture, followed by separation of the individualdiastereomers by standard methods, such as fractional crystallization orchromatography. The coupling reaction is often the formation of saltsusing an enantiomerically pure acid or base. The diasteromericderivatives may then be converted to the pure enantiomers by cleavage ofthe added chiral residue. The racemic mixture of the compounds can alsobe separated directly by chromatographic methods utilizing chiralstationary phases, which methods are well known in the art.

Alternatively, any enantiomer of a compound may be obtained bystereoselective synthesis using optically pure starting materials orreagents of known configuration by methods well known in the art.

It will be understood that, as used herein, references to the compoundsof structural formula I are meant to also include the pharmaceuticallyacceptable salts, and also salts that are not pharmaceuticallyacceptable when they are used as precursors to the free compounds ortheir pharmaceutically acceptable salts or in other syntheticmanipulations.

The compounds of the present invention may be administered in the formof a pharmaceutically acceptable salt. The term “pharmaceuticallyacceptable salt” refers to salts prepared from pharmaceuticallyacceptable non-toxic bases or acids including inorganic or organic basesand inorganic or organic acids. Salts of basic compounds encompassedwithin the term “pharmaceutically acceptable salt” refer to non-toxicsalts of the compounds of this invention which are generally prepared byreacting the free base with a suitable organic or inorganic acid.Representative salts of basic compounds of the present inventioninclude, but are not limited to, the following: acetate,benzenesulfonate, benzoate, bicarbonate, bisulfate, bitartrate, borate,bromide, camsylate, carbonate, chloride, clavulanate, citrate,dihydrochloride, edetate, edisylate, estolate, esylate, fumarate,gluceptate, gluconate, glutamate, glycollylarsanilate, hexylresorcinate,hydrabamine, hydrobromide, hydrochloride, hydroxynaphthoate, iodide,isothionate, lactate, lactobionate, laurate, malate, maleate, mandelate,mesylate, methylbromide, methylnitrate, methylsulfate, mucate,napsylate, nitrate, N-methylglucamine ammonium salt, oleate, oxalate,pamoate (embonate), palmitate, pantothenate, phosphate/diphosphate,polygalacturonate, salicylate, stearate, sulfate, subacetate, succinate,tannate, tartrate, teoclate, tosylate, triethiodide and valerate.Furthermore, where the compounds of the invention carry an acidicmoiety, suitable pharmaceutically acceptable salts thereof include, butare not limited to, salts derived from inorganic bases includingaluminum, ammonium, calcium, copper, ferric, ferrous, lithium,magnesium, manganic, mangamous, potassium, sodium, zinc, and the like.Particularly preferred are the ammonium, calcium, magnesium, potassium,and sodium salts. Salts derived from pharmaceutically acceptable organicnon-toxic bases include salts of primary, secondary, and tertiaryamines, cyclic amines, and basic ion-exchange resins, such as arginine,betaine, caffeine, choline, N,N-dibenzylethylenediamine, diethylamine,2-diethylaminoethanol, 2-dimethylaminoethanol, ethanolamine,ethylenediamine, N-ethylmorpholine, N-ethylpiperidine, glucamine,glucosamine, histidine, hydrabamine, isopropylamine, lysine,methylglucamine, morpholine, piperazine, piperidine, polyamine resins,procaine, purines, theobromine, triethylamine, trimethylamine,tripropylamine, tromethamine, and the like.

Also, in the case of a carboxylic acid (—COOH) or alcohol group beingpresent in the compounds of the present invention, pharmaceuticallyacceptable esters of carboxylic acid derivatives, such as methyl, ethyl,or pivaloyloxymethyl, or acyl derivatives of alcohols, such as acetateor maleate, can be employed. Included are those esters and acyl groupsknown in the art for modifying the solubility or hydrolysischaracteristics for use as sustained-release or prodrug formulations.

Solvates, and in particular, the hydrates of the compounds of structuralformula I are included in the present invention as well.

Exemplifying the invention is the use of the compounds disclosed in theExamples and herein.

The subject compounds are useful in a method of inhibiting thedipeptidyl peptidase-IV enzyme in a patient such as a mammal in need ofsuch inhibition comprising the administration of an effective amount ofthe compound. The present invention is directed to the use of thecompounds disclosed herein as inhibitors of dipeptidyl peptidase-IVenzyme activity.

In addition to primates, such as humans, a variety of other mammals canbe treated according to the method of the present invention. Forinstance, mammals including, but not limited to, cows, sheep, goats,horses, dogs, cats, guinea pigs, rats or other bovine, ovine, equine,canine, feline, rodent or murine species can be treated. However, themethod can also be practiced in other species, such as avian species(e.g., chickens).

The present invention is further directed to a method for themanufacture of a medicament for inhibiting dipeptidyl peptidase-IVenzyme activity in humans and animals comprising combining a compound ofthe present invention with a pharmaceutically acceptable carrier ordiluent.

The subject treated in the present methods is generally a mammal,preferably a human being, male or female, in whom inhibition ofdipeptidyl peptidase-IV enzyme activity is desired. The term“therapeutically effective amount” means the amount of the subjectcompound that will elicit the biological or medical response of atissue, system, animal or human that is being sought by the researcher,veterinarian, medical doctor or other clinician.

The term “composition” as used herein is intended to encompass a productcomprising the specified ingredients in the specified amounts, as wellas any product which results, directly or indirectly, from combinationof the specified ingredients in the specified amounts. Such term inrelation to pharmaceutical composition, is intended to encompass aproduct comprising the active ingredient(s), and the inert ingredient(s)that make up the carrier, as well as any product which results, directlyor indirectly, from combination, complexation or aggregation of any twoor more of the ingredients, or from dissociation of one or more of theingredients, or from other types of reactions or interactions of one ormore of the ingredients. Accordingly, the pharmaceutical compositions ofthe present invention encompass any composition made by admixing acompound of the present invention and a pharmaceutically acceptablecarrier. By “pharmaceutically acceptable” it is meant the carrier,diluent or excipient must be compatible with the other ingredients ofthe formulation and not deleterious to the recipient thereof.

The terms “administration of” and or “administering a” compound shouldbe understood to mean providing a compound of the invention or a prodrugof a compound of the invention to the individual in need of treatment.

The utility of the compounds in accordance with the present invention asinhibitors of dipeptidyl peptidase-IV enzyme activity may bedemonstrated by methodology known in the art. Inhibition constants aredetermined as follows. A continuous fluorometric assay is employed withthe substrate Gly-Pro-AMC, which is cleaved by DP-IV to release thefluorescent AMC leaving group. The kinetic parameters that describe thisreaction are as follows: K_(m)=50 μM; k_(cat)=75 s⁻¹;k_(cat)/K_(m)=1.5×10⁶ M⁻¹s⁻¹. A typical reaction contains approximately50 pM enzyme, 50 μM Gly-Pro-AMC, and buffer (100 mM HEPES, pH 7.5, 0.1mg/ml BSA) in a total reaction volume of 100 μl. Liberation of AMC ismonitored continuously in a 96-well plate fluorometer using anexcitation wavelength of 360 nm and an emission wavelength of 460 nm.Under these conditions, approximately 0.8 [M AMC is produced in 30minutes at 25 degrees C. The enzyme used in these studies was soluble(transmembrane domain and cytoplasmic extension excluded) human proteinproduced in a baculovirus expression system (Bac-To-Bac, Gibco BRL). Thekinetic constants for hydrolysis of Gly-Pro-AMC and GLP-1 were found tobe in accord with literature values for the native enzyme. To measurethe dissociation constants for compounds, solutions of inhibitor in DMSOwere added to reactions containing enzyme and substrate (final DMSOconcentration is 1%). All experiments were conducted at room temperatureusing the standard reaction conditions described above. To determine thedissociation constants (Ki), reaction rates were fit by non-linearregression to the Michaelis-Menton equation for competitive inhibition.The errors in reproducing the dissociation constants are typically lessthan two-fold.

In particular, the compounds of the following examples had activity ininhibiting the dipeptidyl peptidase-IV enzyme in the aforementionedassays, generally with an IC50 of less than about 1 μM. Such a result isindicative of the intrinsic activity of the compounds in use asinhibitors the dipeptidyl peptidase-IV enzyme activity.

Dipeptidyl peptidase-IV enzyme (DP-IV) is a cell surface protein thathas been implicated in a wide range of biological functions. It has abroad tissue distribution (intestine, kidney, liver, pancreas, placenta,thymus, spleen, epithelial cells, vascular endothelium, lymphoid andmyeloid cells, serum), and distinct tissue and cell-type expressionlevels. DP-IV is identical to the T cell activation marker CD26, and itcan cleave a number of immunoregulatory, endocrine, and neurologicalpeptides in vitro. This has suggested a potential role for thispeptidase in a variety of disease processes in humans or other species.

Accordingly, the subject compounds are useful in a method for theprevention or treatment of the following diseases, disorders andconditions.

Type II Diabetes and Related Disorders: It is well established that theincretins GLP-1 and GIP are rapidly inactivated in vivo by DP-IV.Studies with DP-IV^((−/−))-deficient mice and preliminary clinicaltrials indicate that DP-IV inhibition increases the steady stateconcentrations of GLP-1 and GIP, resulting in improved glucosetolerance. By analogy to GLP-1 and GIP, it is likely that other glucagonfamily peptides involved in glucose regulation are also inactivated byDP-IV (eg. PACAP). Inactivation of these peptides by DP-IV may also playa role in glucose homeostasis.

The DP-IV inhibitors of the present invention therefore have utility inthe treatment of type II diabetes and in the treatment and prevention ofthe numerous conditions that often accompany Type II diabetes, includingSyndrome X (also known as Metabolic Syndrome), reactive hypoglycemia,and diabetic dyslipidemia. Obesity, discussed below, is anothercondition that is often found with Type II diabetes that may respond totreatment with the compounds of this invention. In Syndrome X, alsoknown as Metabolic Syndrome, obesity is thought to promote insulinresistance, diabetes, dyslipidemia, hypertension, and increasedcardiovascular risk. Therefore, DP-IV inhibitors may also be useful totreat hypertension associated with this condition.

The following diseases, disorders and conditions are related to Type 2diabetes, and therefore may be treated, controlled or in some casesprevented, by treatment with the compounds of this invention: (1)hyperglycemia, (2) low glucose tolerance, (3) insulin resistance, (4)obesity, (5) lipid disorders, (6) dyslipidemia, (7) hyperlipidemia, (8)hypertriglyceridemia, (9) hypercholesterolemia, (10) low HDL levels,(11) high LDL levels, (12) atherosclerosis and its sequelae, (13)vascular restenosis, (14) irritable bowel syndrome, (15) inflammatorybowel disease, including Crohn's disease and ulcerative colitis, (16)other inflammatory conditions, (17) pancreatitis, (18) abdominalobesity, (19) neurodegenerative disease, (20) retinopathy, (21)nephropathy, (22) neuropathy, (23) Syndrome X, (24) ovarianhyperandrogenism (polycystic ovarian syndrome), and other disorderswhere insulin resistance is a component.

Obesity: DP-IV inhibitors may be useful for the treatment of obesity.This is based on the observed inhibitory effects on food intake andgastric emptying of GLP-1 and GLP-2. Exogenous administration of GLP-1in humans significantly decreases food intake and slows gastric emptying(Am. J. Physiol., 277: R910-R916 (1999)). ICV administration of GLP-1 inrats and mice also has profound effects on food intake (Nature Medicine,2: 1254-1258 (1996)). This inhibition of feeding is not observed inGLP-1R^((−/−)) mice, indicating that these effects are mediated throughbrain GLP-1 receptors. By analogy to GLP-1, it is likely that GLP-2 isalso regulated by DP-IV. ICV administration of GLP-2 also inhibits foodintake, analogous to the effects observed with GLP-1 (Nature Medicine,6: 802-807 (2000)). In addition, studies with DP-IV deficient micesuggest that these animals are resistant to diet-induced obesity andassociated pathology (e.g. hyperinsulinonemia).

Growth Hormone Deficiency: DP-IV inhibition may be useful for thetreatment of growth hormone deficiency, based on the hypothesis thatgrowth-hormone releasing factor (GRF), a peptide that stimulates releaseof growth hormone from the anterior pituitary, is cleaved by the DP-IVenzyme in vivo (WO 00/56297). The following data provide evidence thatGRF is an endogenous substrate: (1) GRF is efficiently cleaved in vitroto generate the inactive product GRF[3-44] (BBA 1122: 147-153 (1992));(2) GRF is rapidly degraded in plasma to GRF[3-44]; this is prevented bythe DP-IV inhibitor diprotin A; and (3) GRF[3-44] is found in the plasmaof a human GRF transgenic pig (J. Clin. Invest., 83: 1533-1540 (1989)).Thus DP-IV inhibitors may be useful for the same spectrum of indicationswhich have been considered for growth hormone secretagogues.

Intestinal Iniury: The potential for using DP-IV inhibitors for thetreatment of intestinal injury is suggested by the results of studiesindicating that glucagon-like peptide-2 (GLP-2), a likely endogenoussubstrate for DP-IV, may exhibit trophic effects on the intestinalepithelium (Regulatory Peptides, 90: 27-32 (2000)). Administration ofGLP-2 results in increased small bowel mass in rodents and attenuatesintestinal injury in rodent models of colitis and enteritis.

Immunosuppression: DP-IV inhibition may be useful for modulation of theimmune response, based upon studies implicating the DP-IV enzyme in Tcell activation and in chemokine processing, and efficacy of DP-IVinhibitors in in vivo models of disease. DP-IV has been shown to beidentical to CD26, a cell surface marker for activated immune cells. Theexpression of CD26 is regulated by the differentiation and activationstatus of immune cells. It is generally accepted that CD26 functions asa co-stimulatory molecule in in vitro models of T cell activation. Anumber of chemokines contain proline in the penultimate position,presumably to protect them from degradation by non-specificaminopeptidases. Many of these have been shown to be processed in vitroby DP-IV. In several cases (RANTES, LD78-beta, MDC, eotaxin,SDF-1alpha), cleavage results in an altered activity in chemotaxis andsignaling assays. Receptor selectivity also appears to be modified insome cases (RANTES). Multiple N-terminally truncated forms of a numberof chemokines have been identified in in vitro cell culture systems,including the predicted products of DP-IV hydrolysis.

DP-IV inhibitors have been shown to be efficacious immunosuppressants inanimal models of transplantation and arthritis. Prodipine(Pro-Pro-diphenyl-phosphonate), an irreversible inhibitor of DP-IV, wasshown to double cardiac allograft survival in rats from day 7 to day 14(Transplantation, 63: 1495-1500 (1997)). DP-IV inhibitors have beentested in collagen and alkyldiamine-induced arthritis in rats and showeda statistically significant attenuation of hind paw swelling in thismodel [Int. J. Immunopharmacology, 19:15-24 (1997) andImmunopharmacology, 40: 21-26 (1998)]. DP-IV is upregulated in a numberof autoimmune diseases including rheumatoid arthritis, multiplesclerosis, Graves' disease, and Hashimoto's thyroiditis (ImmunologyToday, 20: 367-375 (1999)).

HIV Infection: DP-IV inhibition may be useful for the treatment orprevention of HIV infection or AIDS because a number of chemokines whichinhibit HIV cell entry are potential substrates for DP-IV (ImmunologyToday 20: 367-375 (1999)). In the case of SDF-1alpha, cleavage decreasesantiviral activity (PNAS, 95: 6331-6 (1998)). Thus, stabilization ofSDF-1alpha through inhibition of DP-IV would be expected to decrease HIVinfectivity.

Hematopoiesis: DP-IV inhibition may be useful for the treatment orprevention of hematopiesis because DP-IV may be involved inhematopoiesis. A DP-IV inhibitor, Val-Boro-Pro, stimulated hematopoiesisin a mouse model of cyclophosphamide-induced neutropenia (WO 99/56753).

Neuronal Disorders: DP-IV inhibition may be useful for the treatment orprevention of various neuronal or psychiatric disorders because a numberof peptides implicated in a variety of neuronal processes are cleaved invitro by DP-IV. A DP-UV inhibitor thus may have a therapeutic benefit inthe treatment of neuronal disorders. Endomorphin-2, beta-casomorphin,and substance P have all been shown to be in vitro substrates for DP-IV.In all cases, in vitro cleavage is highly efficient, with k_(cat)/K_(m)about 10⁶ M⁻¹s⁻¹ or greater. In an electric shock jump test model ofanalgesia in rats, a DP-IV inhibitor showed a significant effect thatwas independent of the presence of exogenous endomorphin-2 (BrainResearch, 815: 278-286 (1999)).

Neuroprotective and neuroregenerative effects of DP-IV inhibitors werealso evidenced by the inhibitors' ability to protect motor neurons fromexcitotoxic cell death, to protect striatal innervation of dopaminergicneurons when administered concurrently with MPTP, and to promoterecovery of striatal innervation density when given in a therapeuticmanner following MPTP treatment [see Yong-Q. Wu, et al.,“Neuroprotective Effects of Inhibitors of Dipeptidyl Peptidase-IV InVitro and In Vivo,” Int. Conf. On Dipeptidyl Aminopeptidases: BasicScience and Clinical Applications, Sep. 26-29, 2002 (Berlin, Germany)].

Tumor Invasion and Metastasis: DP-IV inhibition may be useful for thetreatment or prevention of tumor invasion and metastasis because anincrease or decrease in expression of several ectopeptidases includingDP-IV has been observed during the transformation of normal cells to amalignant phenotype (J. Exp. Med., 190: 301-305 (1999)). Up- ordown-regulation of these proteins appears to be tissue and cell-typespecific. For example, increased CD26/DP-IV expression has been observedon T cell lymphoma, T cell acute lymphoblastic leukemia, cell-derivedthyroid carcinomas, basal cell carcinomas, and breast carcinomas. Thus,DP-IV inhibitors may have utility in the treatment of such carcinomas.

Benign Prostatic Hypertrophy: DP-IV inhibition may be useful for thetreatment of benign prostatic hypertrophy because increased DP-IVactivity was noted in prostate tissue from patients with BPH (Eur. J.Clin. Chem. Clin. Biochem., 30: 333-338 (1992)).

Sperm motility/male contraception: DP-IV inhibition may be useful forthe altering sperm motility and for male contraception because inseminal fluid, prostatosomes, prostate derived organelles important forsperm motility, possess very high levels of DP-IV activity (Eur. J.Clin. Chem. Clin. Biochem., 30: 333-338 (1992)).

Gingivitis: DP-IV inhibition may be useful for the treatment ofgingivitis because DP-IV activity was found in gingival crevicular fluidand in some studies correlated with periodontal disease severity (Arch.Oral Biol., 37: 167-173 (1992)).

Osteoporosis: DP-IV inhibition may be useful for the treatment orprevention of osteoporosis because GIP receptors are present inosteoblasts.

The compounds of the present invention have utility in treating orpreventing one or more of the following conditions or diseases: (1)hyperglycemia, (2) low glucose tolerance, (3) insulin resistance, (4)obesity, (5) lipid disorders, (6) dyslipidemia, (7) hyperlipidemia, (8)hypertriglyceridemia, (9) hypercholesterolemia, (10) low HDL levels,(11) high LDL levels, (12) atherosclerosis and its sequelae, (13)vascular restenosis, (14) irritable bowel syndrome, (15) inflammatorybowel disease, including Crohn's disease and ulcerative colitis, (16)other inflammatory conditions, (17) pancreatitis, (18) abdominalobesity, (19) neurodegenerative disease, (20) retinopathy, (21)nephropathy, (22) neuropathy, (23) Syndrome X, (24) ovarianhyperandrogenism (polycystic ovarian syndrome), (25) Type II diabetes,(26) growth hormone deficiency, (27) neutropenia, (28) neuronaldisorders, (29) tumor metastasis, (30) benign prostatic hypertrophy,(32) gingivitis, (33) hypertension, (34) osteoporosis, and otherconditions that may be treated or prevented by inhibition of DP-IV.

The subject compounds are further useful in a method for the preventionor treatment of the aforementioned diseases, disorders and conditions incombination with other agents.

The compounds of the present invention may be used in combination withone or more other drugs in the treatment, prevention, suppression oramelioration of diseases or conditions for which compounds of Formula Ior the other drugs may have utility, where the combination of the drugstogether are safer or more effective than either drug alone. Such otherdrug(s) may be administered, by a route and in an amount commonly usedtherefor, contemporaneously or sequentially with a compound of FormulaI. When a compound of Formula I is used contemporaneously with one ormore other drugs, a pharmaceutical composition in unit dosage formcontaining such other drugs and the compound of Formula I is preferred.However, the combination therapy may also include therapies in which thecompound of Formula I and one or more other drugs are administered ondifferent overlapping schedules. It is also contemplated that when usedin combination with one or more other active ingredients, the compoundsof the present invention and the other active ingredients may be used inlower doses than when each is used singly. Accordingly, thepharmaceutical compositions of the present invention include those thatcontain one or more other active ingredients, in addition to a compoundof Formula I.

Examples of other active ingredients that may be administered incombination with a compound of Formula I, and either administeredseparately or in the same pharmaceutical composition, include, but arenot limited to:

-   -   (a) other dipeptidyl peptidase IV (DP-IV) inhibitors;    -   (b) insulin sensitizers including (i) PPARy agonists such as the        glitazones (e.g. troglitazone, pioglitazone, englitazone,        MCC-555, rosiglitazone, and the like) and other PPAR ligands,        including PPARα/γ dual agonists, such as KRP-297, and PPARα        agonists such as fenofibric acid derivatives (gemfibrozil,        clofibrate, fenofibrate and bezafibrate), (ii) biguanides such        as metformin and phenformin, and (iii) protein tyrosine        phosphatase-1B (PTP-1B) inhibitors;    -   (c) insulin or insulin mimetics;    -   (d) sulfonylureas and other insulin secretagogues, such as        tolbutamide glyburide, glipizide, glimepiride, and meglitinides,        such as repaglinide;    -   (e) α-glucosidase inhibitors (such as acarbose and miglitol);    -   (f) glucagon receptor antagonists such as those disclosed in WO        98/04528, WO 99/01423, WO 00/39088, and WO 00/69810;    -   (g) GLP-1, GLP-1 mimetics, and GLP-1 receptor agonists such as        those disclosed in WO 00/42026 and WO 00/59887;    -   (h) GIP and GIP mimetics such as those disclosed in WO 00/58360,        and GIP receptor agonists;    -   (i) PACAP, PACAP mimetics, and PACAP receptor agonists such as        those disclosed in WO 01/23420;    -   (j) cholesterol lowering agents such as (i) HMG-COA reductase        inhibitors (lovastatin, simvastatin, pravastatin, cerivastatin,        fluvastatin, atorvastatin, itavastatin, and rosuvastatin, and        other statins), (ii) sequestrants (cholestyramine, colestipol,        and dialkylaminoalkyl derivatives of a cross-linked        dextran), (iii) nicotinyl alcohol, nicotinic acid or a salt        thereof, (iv) PPARα (X agonists such as fenofibric acid        derivatives (gemfibrozil, clofibrate, fenofibrate and        bezafibrate), (v) PPARα/γ dual agonists, such as KRP-297, (vi)        inhibitors of cholesterol absorption, such as beta-sitosterol        and ezetimibe, (vii) acyl CoA:cholesterol acyltransferase        inhibitors, such as avasimibe, and (viii) anti-oxidants, such as        probucol;    -   (k) PPARδ agonists, such as those disclosed in WO 97/28149;    -   (l) antiobesity compounds such as fenfluramine, dexfenfluramine,        phentermine, sibutramine, orlistat, neuropeptide Y₁ or Y₅        antagonists, CB1 receptor inverse agonists and antagonists, β₃        adrenergic receptor agonists, melanocortin receptor agonists, in        particular melanocortin-4 receptor agonists, ghrelin        antagonists, and melanin-concentrating hormone (MCH) receptor        antagonists;    -   (m) ileal bile acid transporter inhibitors;    -   (n) agents intended for use in inflammatory conditions such as        aspirin, non-steroidal anti-inflammatory drugs, glucocorticoids,        azulfidine, and selective cyclooxygenase-2 inhibitors;    -   (o) antihypertensive agents such as ACE inhibitors (enalapril,        lisinopril, captopril, quinapril, tandolapril), A-II receptor        blockers (losartan, candesartan, irbesartan, valsartan,        telmisartan, eprosartan), beta blockers and calcium channel        blockers; and    -   (p) glucokinase activators (GKAs).

Dipeptidyl peptidase-IV inhibitors that can be combined with compoundsof structural formula I include those disclosed in WO 03/004498 (16 Jan.2003); WO 03/004496 (16 Jan. 2003); EP 1 258 476 (20 Nov. 2002); WO02/083128 (24 Oct. 2002); WO 02/062764 (15 Aug. 2002); WO 03/000250 (3Jan. 2003); WO 03/002530 (9 Jan. 2003); WO 03/002531 (9 Jan. 2003); WO03/002553 (9 Jan. 2003); WO 03/002593 (9 Jan. 2003); WO 03/000180 (3Jan. 2003); and WO 03/000181 (3 Jan. 2003). Specific DP-IV inhibitorcompounds include isoleucine thiazolidide; NVP-DPP728; P32/98; and LAF237.

Antiobesity compounds that can be combined with compounds of structuralformula I include fenfluramine, dexfenfluramine, phentermine,sibutramine, orlistat, neuropeptide Y₁ or Y₅ antagonists, cannabinoidCB1 receptor antagonists or inverse agonists, melanocortin receptoragonists, in particular, melanocortin-4 receptor agonists, ghrelinantagonists, and melanin-concentrating hormone (MCH) receptorantagonists. For a review of anti-obesity compounds that can be combinedwith compounds of structural formula I, see S. Chaki et al., “Recentadvances in feeding suppressing agents: potential therapeutic strategyfor the treatment of obesity,” Expert Opin. Ther. Patents, 11: 1677-1692(2001) and D. Spanswick and K. Lee, “Emerging antiobesity drugs,” ExpertOpin. Emerging Drugs, 8: 217-237 (2003).

Neuropeptide Y5 antagonists that can be combined with compounds ofstructural formula I include those disclosed in U.S. Pat. No. 6,335,345(1 Jan. 2002) and WO 01/14376 (1 Mar. 2001); and specific compoundsidentified as GW 59884A; GW 569180A; LY366377; and CGP-71683A.

Cannabinoid CB1 receptor antagonists that can be combined with compoundsof formula I include those disclosed in PCT Publication WO 03/007887;U.S. Pat. No. 5,624,941, such as rimonabant; PCT Publication WO02/076949, such as SLV-319; U.S. Pat. No. 6,028,084; PCT Publication WO98/41519; PCT Publication WO 00/10968; PCT Publication WO 99/02499; U.S.Pat. No. 5,532,237; and U.S. Pat. No. 5,292,736.

Melanocortin receptor agonists that can be combined with compounds ofstructural formula I include those disclosed in WO 03/009847 (6 Feb.2003); WO 02/068388 (6 Sep. 2002); WO 99/64002 (16 Dec. 1999); WO00/74679 (14 Dec. 2000); WO 01/70708 (27 Sep. 2001); and WO 01/70337 (27Sep. 2001) as well as those disclosed in J. D. Speake et al., “Recentadvances in the development of melanocortin-4 receptor agonists,” ExpertOpin. Ther. Patents, 12: 1631-1638 (2002).

The potential utility of safe and effective activators of glucokinase(GKAs) for the treatment of diabetes is discussed in J. Grimsby et al.,“Allosteric Activators of Glucokinase: Potential Role in DiabetesTherapy,” Science, 301: 370-373 (2003).

The above combinations include combinations of a compound of the presentinvention not only with one other active compound, but also with two ormore other active compounds. Non-limiting examples include combinationsof compounds having Formula I with two or more active compounds selectedfrom biguanides, sulfonylureas, IMG-CoA reductase inhibitors, PPARagonists, PTP-1B inhibitors, other DP-IV inhibitors, and anti-obesitycompounds.

Likewise, compounds of the present invention may be used in combinationwith other drugs that are used in the treatment/prevention/suppressionor amelioration of the diseases or conditions for which compounds of thepresent invention are useful. Such other drugs may be administered, by aroute and in an amount commonly used therefor, contemporaneously orsequentially with a compound of the present invention. When a compoundof the present invention is used contemporaneously with one or moreother drugs, a pharmaceutical composition containing such other drugs inaddition to the compound of the present invention is preferred.Accordingly, the pharmaceutical compositions of the present inventioninclude those that also contain one or more other active ingredients, inaddition to a compound of the present invention.

The weight ratio of the compound of the present invention to the secondactive ingredient may be varied and will depend upon the effective doseof each ingredient. Generally, an effective dose of each will be used.Thus, for example, when a compound of the present invention is combinedwith another agent, the weight ratio of the compound of the presentinvention to the other agent will generally range from about 1000:1 toabout 1:1000, preferably about 200:1 to about 1:200. Combinations of acompound of the present invention and other active ingredients willgenerally also be within the aforementioned range, but in each case, aneffective dose of each active ingredient should be used.

In such combinations the compound of the present invention and otheractive agents may be administered separately or in conjunction. Inaddition, the administration of one element may be prior to, concurrentto, or subsequent to the administration of other agent(s).

The compounds of the present invention may be administered by oral,parenteral (e.g., intramuscular, intraperitoneal, intravenous, ICV,intracisternal injection or infusion, subcutaneous injection, orimplant), by inhalation spray, nasal, vaginal, rectal, sublingual, ortopical routes of administration and may be formulated, alone ortogether, in suitable dosage unit formulations containing conventionalnon-toxic pharmaceutically acceptable carriers, adjuvants and vehiclesappropriate for each route of administration. In addition to thetreatment of warm-blooded animals such as mice, rats, horses, cattle,sheep, dogs, cats, monkeys, etc., the compounds of the invention areeffective for use in humans.

The pharmaceutical compositions for the administration of the compoundsof this invention may conveniently be presented in dosage unit form andmay be prepared by any of the methods well known in the art of pharmacy.All methods include the step of bringing the active ingredient intoassociation with the carrier which constitutes one or more accessoryingredients. In general, the pharmaceutical compositions are prepared byuniformly and intimately bringing the active ingredient into associationwith a liquid carrier or a finely divided solid carrier or both, andthen, if necessary, shaping the product into the desired formulation. Inthe pharmaceutical composition the active object compound is included inan amount sufficient to produce the desired effect upon the process orcondition of diseases. As used herein, the term “composition” isintended to encompass a product comprising the specified ingredients inthe specified amounts, as well as any product which results, directly orindirectly, from combination of the specified ingredients in thespecified amounts.

The pharmaceutical compositions containing the active ingredient may bein a form suitable for oral use, for example, as tablets, troches,lozenges, aqueous or oily suspensions, dispersible powders or granules,emulsions, hard or soft capsules, or syrups or elixirs. Compositionsintended for oral use may be prepared according to any method known tothe art for the manufacture of pharmaceutical compositions and suchcompositions may contain one or more agents selected from the groupconsisting of sweetening agents, flavoring agents, coloring agents andpreserving agents in order to provide pharmaceutically elegant andpalatable preparations. Tablets contain the active ingredient inadmixture with non-toxic pharmaceutically acceptable excipients whichare suitable for the manufacture of tablets. These excipients may be forexample, inert diluents, such as calcium carbonate, sodium carbonate,lactose, calcium phosphate or sodium phosphate; granulating anddisintegrating agents, for example, corn starch, or alginic acid;binding agents, for example starch, gelatin or acacia, and lubricatingagents, for example magnesium stearate, stearic acid or talc. Thetablets may be uncoated or they may be coated by known techniques todelay disintegration and absorption in the gastrointestinal tract andthereby provide a sustained action over a longer period. For example, atime delay material such as glyceryl monostearate or glyceryl distearatemay be employed. They may also be coated by the techniques described inthe U.S. Pat. Nos. 4,256,108; 4,166,452; and 4,265,874 to form osmotictherapeutic tablets for control release.

Formulations for oral use may also be presented as hard gelatin capsuleswherein the active ingredient is mixed with an inert solid diluent, forexample, calcium carbonate, calcium phosphate or kaolin, or as softgelatin capsules wherein the active ingredient is mixed with water or anoil medium, for example peanut oil, liquid paraffin, or olive oil.

Aqueous suspensions contain the active materials in admixture withexcipients suitable for the manufacture of aqueous suspensions. Suchexcipients are suspending agents, for example sodiumcarboxymethylcellulose, methylcellulose, hydroxy-propylmethylcellulose,sodium alginate, polyvinyl-pyrrolidone, gum tragacanth and gum acacia;dispersing or wetting agents may be a naturally-occurring phosphatide,for example lecithin, or condensation products of an alkylene oxide withfatty acids, for example polyoxyethylene stearate, or condensationproducts of ethylene oxide with long chain aliphatic alcohols, forexample heptadecaethyleneoxycetanol, or condensation products ofethylene oxide with partial esters derived from fatty acids and ahexitol such as polyoxyethylene sorbitol monooleate, or condensationproducts of ethylene oxide with partial esters derived from fatty acidsand hexitol anhydrides, for example polyethylene sorbitan monooleate.The aqueous suspensions may also contain one or more preservatives, forexample ethyl, or n-propyl, p-hydroxybenzoate, one or more coloringagents, one or more flavoring agents, and one or more sweetening agents,such as sucrose or saccharin.

Oily suspensions may be formulated by suspending the active ingredientin a vegetable oil, for example arachis oil, olive oil, sesame oil orcoconut oil, or in a mineral oil such as liquid paraffin. The oilysuspensions may contain a thickening agent, for example beeswax, hardparaffin or cetyl alcohol. Sweetening agents such as those set forthabove, and flavoring agents may be added to provide a palatable oralpreparation. These compositions may be preserved by the addition of ananti-oxidant such as ascorbic acid.

Dispersible powders and granules suitable for preparation of an aqueoussuspension by the addition of water provide the active ingredient inadmixture with a dispersing or wetting agent, suspending agent and oneor more preservatives. Suitable dispersing or wetting agents andsuspending agents are exemplified by those already mentioned above.Additional excipients, for example sweetening, flavoring and coloringagents, may also be present.

The pharmaceutical compositions of the invention may also be in the formof oil-in-water emulsions. The oily phase may be a vegetable oil, forexample olive oil or arachis oil, or a mineral oil, for example liquidparaffin or mixtures of these. Suitable emulsifying agents may benaturally-occurring gums, for example gum acacia or gum tragacanth,naturally-occurring phosphatides, for example soy bean, lecithin, andesters or partial esters derived from fatty acids and hexitolanhydrides, for example sorbitan monooleate, and condensation productsof the said partial esters with ethylene oxide, for examplepolyoxyethylene sorbitan monooleate. The emulsions may also containsweetening and flavoring agents.

Syrups and elixirs may be formulated with sweetening agents, for exampleglycerol, propylene glycol, sorbitol or sucrose. Such formulations mayalso contain a demulcent, a preservative and flavoring and coloringagents.

The pharmaceutical compositions may be in the form of a sterileinjectable aqueous or oleagenous suspension. This suspension may beformulated according to the known art using those suitable dispersing orwetting agents and suspending agents which have been mentioned above.The sterile injectable preparation may also be a sterile injectablesolution or suspension in a non-toxic parenterally-acceptable diluent orsolvent, for example as a solution in 1,3-butane diol. Among theacceptable vehicles and solvents that may be employed are water,Ringer's solution and isotonic sodium chloride solution. In addition,sterile, fixed oils are conventionally employed as a solvent orsuspending medium. For this purpose any bland fixed oil may be employedincluding synthetic mono- or diglycerides. In addition, fatty acids suchas oleic acid find use in the preparation of injectables.

The compounds of the present invention may also be administered in theform of suppositories for rectal administration of the drug. Thesecompositions can be prepared by mixing the drug with a suitablenon-irritating excipient which is solid at ordinary temperatures butliquid at the rectal temperature and will therefore melt in the rectumto release the drug. Such materials are cocoa butter and polyethyleneglycols.

For topical use, creams, ointments, jellies, solutions or suspensions,etc., containing the compounds of the present invention are employed.(For purposes of this application, topical application shall includemouth washes and gargles.)

The pharmaceutical composition and method of the present invention mayfurther comprise other therapeutically active compounds as noted hereinwhich are usually applied in the treatment of the above mentionedpathological conditions.

In the treatment or prevention of conditions which require inhibition ofdipeptidyl peptidase-IV enzyme activity an appropriate dosage level willgenerally be about 0.01 to 500 mg per kg patient body weight per daywhich can be administered in single or multiple doses. Preferably, thedosage level will be about 0.1 to about 250 mg/kg per day; morepreferably about 0.5 to about 100 mg/kg per day. A suitable dosage levelmay be about 0.01 to 250 mg/kg per day, about 0.05 to 100 mg/kg per day,or about 0.1 to 50 mg/kg per day. Within this range the dosage may be0.05 to 0.5, 0.5 to 5 or 5 to 50 mg/kg per day. For oral administration,the compositions are preferably provided in the form of tabletscontaining 1.0 to 1000 mg of the active ingredient, particularly 1.0,5.0, 10.0, 15.0. 20.0, 25.0, 50.0, 75.0, 100.0, 150.0, 200.0, 250.0,300.0, 400.0, 500.0, 600.0, 750.0, 800.0, 900.0, and 1000.0 mg of theactive ingredient for the symptomatic adjustment of the dosage to thepatient to be treated. The compounds may be administered on a regimen of1 to 4 times per day, preferably once or twice per day.

When treating or preventing diabetes mellitus and/or hyperglycemia orhypertriglyceridemia or other diseases for which compounds of thepresent invention are indicated, generally satisfactory results areobtained when the compounds of the present invention are administered ata daily dosage of from about 0.1 mg to about 100 mg per kilogram ofanimal body weight, preferably given as a single daily dose or individed doses two to six times a day, or in sustained release form. Formost large mammals, the total daily dosage is from about 1.0 mg to about1000 mg, preferably from about 1 mg to about 50 mg. In the case of a 70kg adult human, the total daily dose will generally be from about 7 mgto about 350 mg. This dosage regimen may be adjusted to provide theoptimal therapeutic response.

It will be understood, however, that the specific dose level andfrequency of dosage for any particular patient may be varied and willdepend upon a variety of factors including the activity of the specificcompound employed, the metabolic stability and length of action of thatcompound, the age, body weight, general health, sex, diet, mode and timeof administration, rate of excretion, drug combination, the severity ofthe particular condition, and the host undergoing therapy.

Several methods for preparing the compounds of this invention areillustrated in the following Schemes and Examples. Starting materialsare made according to procedures known in the art or as illustratedherein.

The compounds of the present invention can be prepared from beta aminoacid intermediates such as those of formula II and substitutedheterocyclic intermediates such as those of formula III, using standardpeptide coupling conditions followed by deprotection. The preparation ofthese intermediates is described in the following Schemes.

where Ar, X, R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹² and R¹³ are as defined above andP is a suitable nitrogen protecting group such as tert-butoxycarbonyl(BOC), benzyloxycarbonyl (Cbz), or 9-fluorenylmethoxycarbonyl (Fmoc).

Compounds of formula II are commercially available, known in theliterature or may be conveniently prepared by a variety of methodsfamiliar to those skilled in the art. One common route is illustrated inScheme 1. Protected alpha-amino acid 1, which may be commerciallyavailable or readily prepared from the corresponding amino acid byprotection using, for example, di-tert-butyl-dicarbonate (for P=BOC),carbobenzyloxy chloride (for P=Cbz), orN-(9-fluorenylmethoxycarbonyloxy)succinimide (for P=Fmoc), is treatedwith isobutyl chloroformate and a base such as triethylamine ordiisopropylethylamine, followed by diazomethane. The resultantdiazoketone is then treated with silver benzoate in a solvent such asmethanol or aqueous dioxane and may be subjected to sonication followingthe procedure of Sewald et al., Synthesis, 837 (1997) in order toprovide the beta amino acid II. As will be understood by those skilledin the art, for the preparation of enantiomerically pure beta aminoacids II, enantiomerically pure alpha amino acids 1 may be used.Alternate routes to the protected beta-amino acid intermediates II canbe found in the following reviews: E. Juaristi, EnantioselectiveSynthesis of β-Amino Acids, Ed., Wiley-VCH, New York: 1997; Juaristi etal., Aldrichimica Acta, 27: 3 (1994); and Cole et al., Tetrahedron, 32:9517 (1994).

The optionally substituted heterocyclic intermediates of formula III arecommercially available, known in the literature or may be convenientlyprepared by a variety of methods familiar to those skilled in the art.One convenient method for the synthesis of IIIa wherein R¹¹, R¹² and R¹³are hydrogen is shown in Scheme 2. Unsaturated derivative 2 is reduced,for example, by treatment with hydrogen gas and a catalyst such aspalladium on carbon or platinum oxide in a solvent such as methanol orethanol to provide Compound IIIa.

Intermediate 2 is commercially available, known in the literature or maybe conveniently prepared by a variety of methods familiar to thoseskilled in the art. One convenient method for Intermediates 2a, whereinX is N, is illustrated in Scheme 3. Aminopyrazine 3, which iscommercially available, known in the literature or may be convenientlyprepared by a variety of methods familiar to those skilled in the art,is treated with an activated carboxylate derivative such as acidchloride 4 or anhydride 5, conveniently in the presence of a base suchas triethylamine in a solvent such as dichloromethane, to provide amide6. The amide is treated with phosphorus pentachloride at elevatedtemperatures, conveniently in refluxing dichloroethane, to provide theimidoyl chloride 7. Treatment with hydroxylamine provides intermediate8, which may be cyclized to the desired heterocycle 2a by heating inpolyphosphoric acid (PPA) or superphosphoric acid (superphos).

An alternate route to heterocycle 2a, wherein X is N, is shown in Scheme4. Intermediate 6, prepared as described above in Scheme 3, is treatedwith an aminating reagent such asO-trimethylbenzenesulfonylhydroxylamine (9) to provide theaminopyrazonium salt 10. Cyclization with PPA provides heterocycle 2a.

An alternate method for preparing heterocycle III, wherein R⁸ is not H,is illustrated in Scheme 5. Heterocycle IIIb is protected, for example,as a carbamate such as a tert-butyl carbamate (BOC) by treatment withdi-tert-butyl dicarbonate to provide carbamate 11. Followingdeprotonation with a strong base such as sec-butyl lithium or n-butyllithium in the presence of TMEDA, the resultant anion is treated with anelectrophile such as an alkyl halide or aldehyde to provide heterocycle12. The process may be repeated to install a second alkyl group, R¹¹.The carbamate protecting group is then removed, in the case of BOC, bytreatment with an acid such as hydrogen chloride in methanol ortrifluoroacetic acid in dichloromethane, to provide the desiredheterocycle III.

Intermediates II and III are coupled under standard peptide couplingconditions, for example, using1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-hydroxybenzotriazole(EDC/HOBT) or O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumhexafluorophosphate and 1-hydroxy-7-azabenzotriazole (HATU/HOAT) in asolvent such as N,N-dimethylformamide (DMF) or dichloromethane for 3 to48 hours at ambient temperature to provide Intermediate 13 as shown inScheme 6. In some cases, Intermediate III may be a salt, such as ahydrochloride or trifluoroacetic acid salt, and in these cases it isconvenient to add a base, generally N,N-diisopropylethylamine, to thecoupling reaction. The protecting group is then removed with, forexample, trifluoroacetic acid or methanolic hydrogen chloride in thecase of Boc to give the desired amine I. The product is purified fromunwanted side products, if necessary, by recrystallization, trituration,preparative thin layer chromatography, flash chromatography on silicagel, such as with a Biotage® apparatus, or HPLC. Compounds that arepurified by HPLC may be isolated as the corresponding salt. Purificationof intermediates is achieved in the same manner.

In some cases the product I, prepared as described in Scheme 6, may befurther modified, for example, by manipulation of substituents on X, R¹,R⁸, R⁹, R¹⁰, R¹¹, R¹², or R¹³. These manipulations may include, but arenot limited to, reduction, oxidation, alkylation, acylation, andhydrolysis reactions which are commonly known to those skilled in theart.

In some cases intermediates described in the above schemes may befurther modified before the sequences are completed, for example, bymanipulation of substituents on X, R¹, R⁸, R⁹, R¹⁰, R¹ ¹, R¹², or R¹³.These manipulations may include, but are not limited to, reduction,oxidation, alkylation, acylation, and hydrolysis reactions which arecommonly known to those skilled in the art. One such example isillustrated in Scheme 7. Intermediate 12a, wherein R⁸ contains ahydroxyl group, may be treated with (diethylamino)sulfur trifluoride(DAST) to provide the fluoro intermediate 12b. Intermediate 12b isconverted to Intermediate III as described in Scheme 5.

Another example is illustrated in Scheme 8. Intermediate 12a, wherein R⁸is CHOHR^(8′), is dehydrated, conveniently by treatment with1,1-thiocarbonyldiimidazole in the presence of a catalytic amount ofdimethylaminopyridine (DMAP), to give olefin 12c. Reduction of theolefin, for example by treatment with hydrogen over a catalyst such aspalladium on carbon, provides the desired intermediate 12d. Intermediate12d is converted to Intermediate III as described in Scheme 5.

Scheme 9 illustrates another such example. Intermediate 12e wherein R⁸is benzyloxymethyl is reductively hydrogenated, for example, bytreatment with hydrogen in the presence of a catalyst such as palladiumon carbon, to provide alcohol 12f. The alcohol is converted to thecorresponding mesylate 12g by treatment with mesyl chloride and a basesuch as triethylamine. The mesylate may be displaced with a variety ofelectrophiles, conveniently in the presence of a base. One suchelectrophile, illustrated in Scheme 9, is triazole 14, which may bereacted in the presence of potassium carbonate in a solvent such asN,N-dimethylformamide to provide the triazolylmethyl intermediate 12h.Intermediate 12h is converted into Intermediate III as described inScheme 5.

In some cases the order of carrying out the foregoing reaction schemesmay be varied to facilitate the reaction or to avoid unwanted reactionproducts. The following examples are provided so that the inventionmight be more fully understood. These examples are illustrative only andshould not be construed as limiting the invention in any way.

(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,5-difluorophenyl)butanoic acidStep A: (R,S)-N-(tert-Butoxycarbonyl)-2,5-difluorophenylalanine

To a solution of 0.5 g (2.49 mmol) of 2,5-difluoro-DL-phenylalanine in 5mL of tert-butanol were added sequentially 1.5 mL of 2N aqueous sodiumhydroxide solution and 543 mg of di-tert-butyl dicarbonate. The reactionwas stirred at ambient temperature for 16 h and diluted with ethylacetate. The organic phase was washed sequentially with 1N hydrochloricacid and brine, dried over magnesium sulfate and concentrated in vacuo.The crude material was purified by flash chromatography (silica gel,97:2:1 dichloromethane:methanol:acetic acid) to afford 671 mg of thetitle compound. MS 302 (M+1).

Step B:(R,S)-3-[(tert-Butoxycarbonyl)amino]-1-diazo-4-(2,5-difluoro-phenyl)butan-2-one

To a solution of 2.23 g (7.4 mmol) of(R,S)-N-(tert-butoxycarbonyl)-2,5-difluorophenylalanine in 100 mL ofdiethyl ether at 0° C. were added sequentially 1.37 mL (8.1 mmol) oftriethylamine and 0.931 mL (7.5 mmol) of isobutyl chloroformate and thereaction was stirred at this temperature for 15 min. A cooled etherealsolution of diazomethane was then added until the yellow color persistedand stirring was continued for a further 16 h. The excess diazomethanewas quenched by dropwise addition of acetic acid, and the reaction wasdiluted with ethyl acetate and washed sequentially with 5% hydrochloricacid, saturated aqueous sodium bicarbonate solution and brine, driedover magnesium sulfate and concentrated in vacuo. Purification by flashchromatography (silica gel, 4:1 hexane:ethyl acetate) afforded 1.5 g ofdiazoketone.

¹H NMR (500 MHz, CDCl₃) δ 7.03-6.95 (m, 1H), 6.95-6.88 (m, 2H), 5.43(bs, 1H), 5.18 (bs, 1H), 4.45 (bs, 1H), 3.19-3.12 (m, 1H), 2.97-2.80 (m,1H), 1.38 (s, 9H).

Step C:(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,5-difluorophenyl)butanoic acid

To a solution of 2.14 g (6.58 mmol) of(R,S)-3-[(tert-butoxycarbonyl)-amino]-1-diazo-4-(2,5-difluorophenyl)butan-2-onedissolved in 100 mL of methanol at −30° C. were added sequentially 3.3mL (19 mmol) of diisopropylethylamine and 302 mg (1.32 mmol) of silverbenzoate. The reaction was stirred for 90 min before diluting with ethylacetate and washing sequentially with 2N hydrochloric acid, saturatedaqueous sodium bicarbonate, and brine. The organic phase was dried overmagnesium sulfate, concentrated in vacuo and the enantiomers wereseparated by preparative chiral HPLC (Chiralpak AD column, 5% ethanol inhexanes) to give 550 mg of the desired (R)-enantiomer, which elutedfirst. This material was dissolved in 50 mL of a mixture oftetrahydrofuran:methanol: 1N aqueous lithium hydroxide (3:1:1) andstirred at 50° C. for 4 h. The reaction was cooled, acidified with 5%dilute hydrochloric acid and extracted with ethyl acetate. The combinedorganic phases were washed with brine, dried over magnesium sulfate andconcentrated in vacuo to give 360 mg of the title compound as a whitefoamy solid.

¹H NMR (500 MHz, CDCl₃) δ 7.21 (m, 1H), 6.98 (m, 2H), 6.10 (bs, 1H),5.05 (m, 1H), 4.21 (m, 1H), 2.98 (m, 2H), 2.60 (m, 2H), 1.38 (s, 9H).

(3R)-3-[(tert-Butoxycarbonyl)amino]-4-[2-fluoro-4-(trifluoromethyl)phenyl]-butanoicacid Step A:(2R,5S)-2,5-Dihydro-3,6-dimethoxy-2-(2′-fluoro-4′-(trifluoromethyl)benzyl)-5-isopropylpyrazine

To a solution of 3.32 g (18 mmol) of commercially available(2S)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine in 100 mL oftetrahydrofuran at −70° C. was added 12 mL (19 mmol) of a 1.6M solutionof butyllithium in hexanes. After stirring at this temperature for 20min, 5 g (19.5 mmol) of 2-fluoro-4-trifluoromethylbenzyl bromide in 20mL of tetrahydrofuran was added and stirring was continued for 3 hbefore warming the reaction to ambient temperature. The reaction wasquenched with water, concentrated in vacuo, and extracted with ethylacetate. The combined organic phase was washed with brine, dried, andconcentrated in vacuo. Purification by flash chromatography (silica gel,0-5% ethyl acetate in hexanes) afforded 5.5 g of the title compound.

¹H NMR (500 MHz, CDCl₃) δ 7.33-7.25 (m, 3H), 4.35-4.31 (m, 1H), 3.75 (s,3H), 3.65 (s, 3H), 3.60 (t, 1H, J=3.4 Hz), 3.33 (dd, 1H, J=4.6, 13.5Hz), 3.03 (dd, 1H, J=7, 13.5 Hz), 2.25-2.15 (m, 1H), 1.0 (d, 3H, J=7Hz), 0.66 (d, 3H, J=7 Hz).

Step B:(R)-N-(tert-Butoxycarbonyl)-2-fluoro-4-trifluoromethyl-phenylalaninemethyl ester

To a solution of 5.5 g (15 mmol) of(2R,5S)-2,5-dihydro-3,6-dimethoxy-2-(2′-fluoro-4′-(trifluoromethyl)benzyl)-5-isopropylpyrazinein 50 mL of a mixture of acetonitrile:dichloromethane (10:1) was added80 mL of 1N aqueous trifluoroacetic acid. The reaction was stirred for 6h and the organic solvents were removed in vacuo. Sodium carbonate wasadded until the solution was basic (>pH 8), and then the reaction wasdiluted with 100 mL of tetrahydrofuran and 10 g (46 mmol) ofdi-tert-butyl dicarbonate was added. The resulting slurry was stirredfor 16 h, concentrated in vacuo, and extracted with ethyl acetate. Thecombined organic phase was washed with brine, dried, and concentrated invacuo. Purification by flash chromatography (silica gel, 20% ethylacetate in hexanes) afforded 5.1 g of the title compound.

¹H NMR (500 MHz, CDCl₃) δ 7.38-7.28 (m, 3H), 5.10 (bd, 1H), 4.65-3.98(m, 1H), 3.76 (s, 3H), 3.32-3.25 (m, 1H), 3.13-3.05 (m, 1H), 1.40 (s,9H).

Step C:(R)-N-(tert-Butoxycarbonyl)-2-fluoro-4-trifluoromethyl)phenyl-alanine

A solution of 5.1 g (14 mmol) of(R,S)-N-(tert-butoxycarbonyl)-2-fluoro-4-trifluoromethyl)phenylalaninemethyl ester in 350 mL of a mixture of tetrahydrofuran:methanol:1Nlithium hydroxide (3:1:1) was stirred at 50° C. for 4 h. The reactionwas cooled, acidified with 5% hydrochloric acid and extracted with ethylacetate. The combined organic phases were washed with brine, dried overmagnesium sulfate and concentrated in vacuo to give 4.8 g of the titlecompound.

¹H NMR (500 MHz, CD₃OD) δ 7.45-7.38 (m, 3H), 4.44-4.40 (m, 1H),3.38-3.33 (m, 1H), 2.98 (dd, 1H, J=9.6, 13.5 Hz), 1.44 (s, 9H).

Step D:(3R)-3-[(tert-Butoxycarbonyl)amino]-4-[2-fluoro-4-(trifluoromethyl)-phenyl]-butanoicacid

To a solution of 3.4 g (9.7 mmol) of the product from Step C in 60 mL oftetrahydrofuran at 0° C. were added sequentially 2.3 mL (13 mmol) ofdiisopropylethylamine and 1.7 mL (13 mmol) of isobutyl chloroformate andthe reaction was stirred at this temperature for 30 min. A cooledethereal solution of diazomethane was then added until the yellow colorpersisted and stirring was continued for a further 16 h. The excessdiazomethane was quenched by dropwise addition of acetic acid, and thereaction was diluted with ethyl acetate and washed sequentially with 5%hydrochloric acid, saturated aqueous sodium bicarbonate solution andbrine, dried over magnesium sulfate and concentrated in vacuo.Purification by flash chromatography (silica gel, 9:1 hexane:ethylacetate) afforded 0.5 g of diazoketone. To a solution of 0.5 g (1.33mmol) of the diazoketone dissolved in 100 mL of methanol at 0° C. wereadded sequentially 0.7 mL (4 mmol) of diisopropylethylamine and 32 mg(0.13 mmol) of silver benzoate. The reaction was stirred for 2 h beforediluting with ethyl acetate and washing sequentially with 2Nhydrochloric acid, saturated aqueous sodium bicarbonate, and brine. Theorganic phase was dried over magnesium sulfate, concentrated in vacuoand dissolved in 50 mL of a mixture of tetrahydrofuran:methanol:1Naqueous lithium hydroxide (3:1:1) and stirred at 50° C. for 3 h. Thereaction was cooled, acidified with 5% hydrochloric acid and extractedwith ethyl acetate. The combined organic phases were washed with brine,dried over magnesium sulfate and concentrated in vacuo to give 410 mg ofthe title compound as a white foamy solid.

¹H NMR (500 MHz, CD₃OD): δ 7.47-7.33 (m, 3H), 4.88 (bs, 1H), 4.26-3.98(m, 1H), 3.06-3.01 (m, 1H), 2.83-2.77 (m, 1H), 2.58-2.50 (m, 2H), 1.29(s, 9H).

(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid Step A:(2S,5R)-2,5-Dihydro-3,6-dimethoxy-2-isopropyl-5-(2′,4′,5′trifluorobenzyl)-pyrazine

The title compound (3.81 g) was prepared from 3.42 g (18.5 mmol) of(2S)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine and 5 g (22.3 mmol)of 2,4,5-trifluorobenzyl bromide using the procedure described forIntermediate 2, Step A.

¹H NMR (500 MHz, CDCl₃): δ 7.01 (m, 1H), 6.85 (m, 1H), 4.22 (m, 1H),3.78 (m, 3H), 3.64 (m, 3H), 3.61 (m, 1H), 3.20 (m, 1H), 2.98 (m, 1H),2.20 (m, 1H), 0.99 (d, 3H, J=8 Hz), 0.62 (d, 3H, J=8 Hz).

Step B: (R)-N-(tert-Butoxycarbonyl)-2,4,5-trifluorophenylalanine methylester

To a solution of 3.81 g (11.6 mmol) of(2S,5R)-2,5-dihydro-3,6-dimethoxy-2-isopropyl-5-(2′,4′,5′trifluorobenzyl)pyrazinein 20 mL of acetonitrile was added 20 mL of 2N hydrochloric acid. Thereaction was stirred for 72 h and concentrated in vacuo. The residue wasdissolved in 30 mL of dichloromethane and 10 mL (72 mmol) oftriethylamine and 9.68 g (44.8 mmol) of di-tert-butyl dicarbonate wereadded. The reaction was stirred for 16 h, diluted with ethyl acetate andwashed sequentially with 1N hydrochloric acid and brine. The organicphase was dried over sodium sulfate, concentrated in vacuo and purifiedby flash chromatography (silica gel, 9:1 hexanes:ethyl acetate) toafford 2.41 g of the title compound.

¹H NMR (500 MHz, CDCl₃): δ 6.99 (m, 1H), 6.94 (m, 1H), 5.08 (m, 1H),4.58 (m, 1H), 3.78 (m, 3R), 3.19 (m, 1H), 3.01 (m, 1H), 1.41 (s, 9H).

Step C: (R)-N-(tert-Butoxycarbonyl)-2,4,5-trifluorophenylalanine

The title compound (2.01 g) was prepared from 2.41 g (7.5 mol) of(R)-N-(tert-butoxycarbonyl)-2,4,5-trifluorophenylalanine methyl esterusing the procedure described for Intermediate 2, Step C. LC-MS 220.9(M+1-BOC).

Step D:(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)-butanoicacid

To a solution of 0.37 g (1.16 mmol) of(R)-N-(1,1-dimethylethoxy-carbonyl)-2,4,5-trifluorophenylalanine in 10mL of diethyl ether at −20° C. were added sequentially 0.193 mL (1.3mmol) of triethylamine and 0.18 mL (1.3 mmol) of isobutyl chloroformate,and the reaction was stirred at this temperature for 15 min. A cooledethereal solution of diazomethane was then added until the yellow colorpersisted and stirring was continued for a further 1 h. The excessdiazomethane was quenched by dropwise addition of acetic acid, and thereaction was diluted with ethyl acetate and washed sequentially withsaturated aqueous sodium bicarbonate solution and brine, dried overmagnesium sulfate and concentrated in vacuo. Purification by flashchromatography (silica gel, 3:1 hexane:ethyl acetate) afforded 0.36 g ofdiazoketone. To a solution of 0.35 g (1.15 mmol) of the diazoketonedissolved in 12 mL of 1,4-dioxane: water (5:1) was added 26 mg (0.113mmol) of silver benzoate. The resultant solution was sonicated for 2 hbefore diluting with ethyl acetate and washing sequentially with 1Nhydrochloric acid and brine, drying over magnesium sulfate andconcentrating in vacuo. Purification by flash chromatography (silicagel, 97:2:1 dichloromethane:methanol:acetic acid) afforded 401 mg of thetitle compound.

¹H NMR (500 MHz, CDCl₃) δ 7.06 (m, 1H), 6.95 (m, 1H), 5.06 (bs, 1H),4.18 (m, 1H), 2.98 (m, 2H), 2.61 (m, 2H), 1.39 (s, 9H).

(3R)-4-(2-Bromo-4,5-difluorophenyl)-3-[(tert-butoxycarbonyl)amino]-butanoicacid

To a solution of 2.4 g (10 mmol) of 2-bromo-4,5-difluorobenzoic acid[prepared according to the procedure of Braish et al., Syn. Comm.,3067-3074 (1992)] in 75 mL of tetrahydrofuran was added 2.43 g (15 mmol)of carbonyldiimidazole. The solution was heated under reflux for 3.5 h,cooled to ambient temperature and 0.38 g (10 mmol) of sodium borohydridein 15 mL of water was added. The reaction was stirred for 10 min andpartitioned between ethyl acetate and 10% aqueous sodium bicarbonatesolution. The organic layer was washed twice with warm water, brine,dried over magnesium sulfate, and concentrated in vacuo. Purification byflash chromatography (silica gel, 4:1 hexane:ethyl acetate) afforded 1.9g of 2-bromo-4,5-difluorobenzyl alcohol. To a solution of 1.9 g (8.4mmol) of 2-bromo-4,5-difluorobenzyl alcohol in 30 mL of dichloromethaneat 0° C. was added 3.4 g (10 mmol) of carbon tetrabromide and 2.7 g (10mmol) of triphenylphosphine. The reaction was stirred for 2 h at thistemperature, the solvent was removed in vacuo and the residue stirredwith 100 mL of diethyl ether. The solution was filtered, concentrated invacuo, and purified by flash chromatography (silica gel, 20:1hexane:ethyl acetate) to afford 2.9 g of 2-bromo-4,5-difluorobenzylbromide contaminated with carbon tetrabromide which was used withoutfurther purification. Using the procedures outlined for the preparationof Intermediates 2-4, the benzyl bromide derivative was converted to thetitle compound. LC-MS 394 and 396 (M+1).

Essentially following the procedures outlined for the preparation ofIntermediates 1-4, the Intermediates in Table 1 were prepared. TABLE 1

Intermediate R³ Selected ¹H NMR data (CD₃OD) 5 2-F,4-Cl,5-F 7.11 (dd, 1H, J=8.9, 6.4 Hz), 7.03 (dd, 1 H, J=9.0, 6.6) 6 2-F,5-Cl 7.27 (dd, 1 H,J=6.4, 2.5 Hz), 7.21 (m, 1 H), 7.03 (t, 1 H, J=9.2 Hz) 7 2-Me,5-Cl 7.16(d, 1 H, J=1.8 Hz), 7.11-7.07 (m, 2 H), 2.34 (s, 3 H) 8 2-Cl,5-Cl 7.34(d, 1 H, J=9.0), 7.33 (d, 1 H, J=2.1 Hz), 7.21 (dd, 1 H, J=8.5, 2.5 Hz)9 2-F,3-Cl,6-F 7.35 (td, 1 H, J=8.5, 5.8 Hz), 6.95 (t, 1 H, J=8.5 Hz) 103-Cl,4-F 7.33 (d, 1 H, J=6.9 Hz), 7.19-7.11 (m, 2 H) 11 2-F,3-F,6-F7.18-7.12 (m, 1 H), 6.91 (m, 1 H) 12 2-F,4-F,6-F 6.81 (t, 2 H, J=8.4 Hz)13 2-OCH₂Ph,5-F 7.49 (d, 2 H, J=7.6 Hz), 7.38 (t, 2 H, J= 7.3 Hz), 7.30(t, 1 H, J=7.3 Hz), 6.96- 6.89 (m, 3 H), 5.11 (d, 1 H, J=11.7 Hz), 5.08(d, 1 H, J=11.9 Hz)

EXAMPLE 1

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride Step A: 2,2,2-Trifluoro-N-pyrazin-2-ylacetamide

To a slightly heterogeneous solution of aminopyrazine (22.74 g, 239mmol) and triethylamine (36.66 mL, 263 mmol) in dichloromethane (400 mL)was added trifluoroacetic anhydride (50.20 g, 239 mmol) dropwise at 0°C. The solution was stirred at 0° C. for 1 h and at ambient temperaturefor 2 h. Filtration of the resultant white precipitate followed bywashing with dichloromethane afforded the title compound as a whitesolid.

¹H NMR (500 MHz, CD₃OD): δ 8.44-8.46 (m, 2H), 9.33 (d,1H, J=1.4 Hz);LC/MS 192 (M+1).

Step B: 2,2,2-Trifluoro-N′-hydroxy-N-pyrazin-2-ylethanimidamide

To a suspension of 2,2,2-trifluoro-N-pyrazin-2-ylacetamide (14.56 g,76.26 mmol, from Step A) in dichloroethane (325 mL) was addedphosphorous pentachloride (421.73 g, 99.13 mmol) portionwise. Themixture was refluxed for 5 h. After evaporation of dichloroethane, theresidue was suspended in tetrahydrofuran (325 mL). To the above mixturewas added 50% aqueous hydroxylamine (20 mL) dropwise. After stirring atambient temperature for 2 h, the mixture was partitioned between ethylacetate and aqueous sodium bicarbonate. The aqueous layer was extractedthree times with ethyl acetate. The combined organic layers were washedwith brine and dried over anhydrous magnesium sulfate. Concentrationgave the title compound as a yellow solid.

¹H-NMR (500 MHz, CD₃OD): δ 8.04 (m, 2H), 8.17 (s, 1H). LC/MS 207 (M+1).

Step C: 2-(Trifluoromethyl)[1,2,4]triazolo[1,5-α]pyrazine

A mixture of 2,2,2-trifluoro-N′-hydroxy-N-pyrazin-2-ylethanimidamide(10.5 g, 50.97 mmol, from Step B) and polyphosphoric acid (80 mL) washeated to 150° C. with stirring for 18 h. The solution was added to iceand neutralized by addition of ammonium hydroxide. The dark aqueoussolution was extracted three times with ethyl acetate, washed withbrine, and dried over anhydrous magnesium sulfate. Concentrationfollowed by flash chromatography (50% then 100% ethyl acetate/hexane)afforded the title compound as a yellow solid.

¹H-NMR (500 MHz, CDCl₃): δ 8.42 (d, 1H, J=4.6 Hz), 8.67 (dd, 1H, J=1.4and 4.6 Hz), 9.47 (d, 1H, J=1.4 Hz). LC/MS 189 (M+1).

Step D:2-(Trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

2-(Trifluoromethyl)-[1,2,4]triazolo[1,5-α]pyrazine (340 mg, 1.81 mmol,from Step C) was hydrogenated under atmospheric hydrogen with 10%palladium on carbon (60 mg) as a catalyst in ethanol (10 mL) at ambienttemperature for 18 h. Filtration through Celite followed byconcentration gave a dark colored oil. Flash chromatography (100% ethylacetate, then 10% methanol/dichloromethane) gave the title compound as awhite solid.

¹H-NMR (500 MHz, CDCl₃): δ 1.80 (br, 1H), 3.40 (t, 2H, J=5.5 Hz),4.22-4.26 (m, 4H); LC/MS 193 (M+1).

Step E:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine

To a solution of2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(28.8 mg, 0.15 mmol, from Step D) and(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid (Intermediate 3, 50.0 mg, 0.15 mmol) in DMF (3 mL) was addedhydroxybenzotriazole (HOBT, 26.1 mg, 0.19 mmol) at 0° C. The reactionwas stirred at 0° C. for 5 min, then1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC, 37.0mg, 0.19 mmol) was added. After removal of the ice-bath, the reactionwas allowed to stir at ambient temperature for 16 h. After removal ofthe DMF by evaporation, the residue was partitioned between ethylacetate and aqueous sodium bicarbonate. The aqueous layer was extractedthree times with ethyl acetate. The combined organic layers were washedwith brine and dried over magnesium sulfate. Concentration followed bypreparative TLC (10% methanol/dichloromethane) gave the title compoundas a foamy solid.

¹H NMR (500 MHz, CDCl₃): δ 1.38 (s, 9H), 2.60-3.00 (m, 4H), 3.95-4.40(m, 5H), 4.84 (s, 1H), 4.95-5.02 (m, 1H), 5.30 (br s, 1H), 6.85-6.95 (m,1H), 7.05-7.13 (m, 1H); LC/MS 408 (M+1-BOC).

Step F:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4triazolo[1,5-α]pyrazine,hydrochloride

To7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine(63.1 mg, 0.12 mmol, from Step E) was added 3 mL of methanol saturatedwith hydrogen chloride at 0° C. The reaction was stirred at ambienttemperature for 45 min. Concentration gave the title compound as a whitesolid.

¹H NMR (500 MHz, CD₃OD): δ 2.75-3.15 (m, 4H), 3.85-3.95 (m, 1H),4.00-4.40 (m, 4H), 4.90-5.00 (m, 2H), 7.18-7.25 (m, 1H), 7.32-7.42 (m,10H). ESI-MS 408 (M+1).

EXAMPLE 2

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride Step A:7-N-(tert-Butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a solution of2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(3.68 g, 19.18 mmol, Step D, Example 1) in 70 mL of dichloromethane wasadded di-tert-butyl dicarbonate (4.60 g, 21.10 mmol) and 3.34 mL (19.18mmol) of diisopropylethylamine. The reaction mixture was allowed to stirat ambient temperature overnight. After evaporation of dichloromethane,the residue was partitioned between saturated aqueous sodium bicarbonatesolution and ethyl acetate. The aqueous phase was extracted with threeportions of ethyl acetate, and the combined organic phases were washedwith brine, dried over magnesium sulfate, and concentrated. Flashchromatography (silica gel, 10% followed by 20% ethyl acetate/hexane)yielded the title compound as a clear oil.

¹H-NMR (500 MHz, CDCl₃): δ 1.51 (s, 9H), 3.99 (t, 2H, J=5.3 Hz), 4.28(t, 2H, J=5.5 Hz), 4.81 (s, 2H); LC/MS 237 (M+1-t-Bu).

Step B:7-N-(tert-Butoxycarbonyl)-8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a solution of7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(1.85 g, 6.35 mmol) in 25 mL of toluene at −78° C. was addedN,N,N,N-tetramethylethylenediamine (1.01 mL, 6.67 mmol) followed byn-butyllithium (4.17 mL of a 1.6 M solution in hexanes, 6.67 mmol). Themixture was stirred at −78° C. for 10 min and then iodomethane (0.415mL, 6.67 mmol) was added dropwise. The mixture was allowed to stir at−78° C. for 10 min, and then it was warmed to ambient temperature. Thereaction was quenched with aqueous ammonium chloride and the aqueouslayer was extracted three times with ethyl acetate. The combined organiclayers were washed with brine, dried over magnesium sulfate, andconcentrated. Purification by flash chromatography (silica gel, 10%ethyl acetate/hexane) yielded the title compound.

¹H-NMR (500 MHz, CDCl₃): δ 1.55 (s, 9H), 1.61 (d, 3H, J=6.9 Hz), 3.40(br 1H), 4.22-4.27 (m, 1H), 4.30-4.35 (m, 1H), 4.62 (br 1H), 5.50 (br1H); LC/MS 251 (M+1-t-Bu).

Step C:8-Methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride

To a solution of7-N-(tert-butoxycarbonyl)-8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(2.40 g, 7.83 mmol) in 40 mL of methanol was added 50 mL of methanolsaturated with hydrogen chloride. The reaction was stirred at ambienttemperature for 1 h. Concentration in vacuo gave the title compound asan off-white solid.

¹H NMR (500 MHz, CD₃OD): δ 1.82 (d, 3H, J=6.8 Hz), 3.82-3.88 (m, 1H),3.98-4.05 (m, 1H), 4.53-4.65 (m, 2H), 4.95 (q, 1H, J=6.9 Hz); LC/MS 207(M+1).

Step D:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine

To a solution of8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride (103 mg, 0.50 mmol, from Step C),(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid (Intermediate 3, 175 mg, 0.53 mmol), and N,N-diisopropylethylamine(0.096 mL, 0.55 mmol) in DMF (1.5 mL) was added1-hydroxy-7-azabenzotriazole (HOAT) (81.7, 0.60 mmol) followed byO-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluroniumhexafluorophosphate (HATU) (228 mg, 0.60 mmol). The solution was stirredat ambient temperature for 24 h. After removal of the DMF byevaporation, the residue was partitioned between ethyl acetate andaqueous sodium bicarbonate. The aqueous layer was extracted three timeswith ethyl acetate. The combined organic layers were washed with brine,dried over anhydrous magnesium sulfate, and concentrated. Purificationby flash chromatography (25% ethyl acetate/hexane) gave the titlecompound as a mixture of diastereomers. The diastereomers were separatedby HPLC (Gilson, OD Chiralcel column, 7% ethyl acetate/hexane). Fastereluting diastereomer: ¹H NMR (500 MHz, CDCl₃) δ 1.38, (s, 9H), 1.50-1.80(m, 3H), 2.45-3.10 (m, 4H), 3.20-3.30 (m, 0.5H), 3.66-3.80 (m, 0.5H),4.05-4.45 (m, 3.5H), 5.10-5.20 (m, 0.5H), 5.20-5.40 (m, 1.5H), 5.90-6.00(m, 0.5H), 6.80-7.00 (m, 1H), 7.02-7.18 (m, 1H); LC/MS 422 (M+1-Boc);Slower eluting diastereomer: ¹H NMR (500 MHz, CDCl₃) δ 1.39, (s, 9H),1.50-1.75 (m, 3H), 2.60-3.05 (m, 4H), 3.20-3.30 (m, 0.5H), 3.65-3.75 (m,0.5H), 4.00-4.40 (m, 3.5H), 5.10-5.18 (m, 0.5H), 5.18-5.42 (m, 1.5H),5.90-5.99 (m, 0.5H), 6.85-6.95 (m, 1H), 6.95-7.15 (m, 1H); LC/MS 422(M+1-BOC).

Step E:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride

To a solution of 46.4 mg of the slower eluting diastereomer of7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-methyl-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazinefrom Step D in 15 mL of methanol was added 20 mL of methanol saturatedwith hydrogen chloride. After 30 min, the reaction was concentrated invacuo to give the title compound as a white solid.

In a separate experiment, to a solution of 46.8 mg of the faster elutingdiastereomer in 5 mL of methanol was added 6 mL of methanol saturatedwith hydrogen chloride. The reaction was stirred at ambient temperaturefor 30 min. Concentration gave the product as a white solid.

Compound from the faster eluting diastereomer: ¹H NMR (500 MHz, CD₃OD) δ1.50-1.75 (m, 3H), 2.80-3.15 (m, 4H), 3.39-3.46 (m, 0.3H), 3.80-3.95 (m,1.7H), 4.19 (dt, 0.3H, J=4.2, 12.6 Hz), 4.23-4.40 (m, 2.4H), 5.00 (dd,0.3H, J=4.3, 14.2 Hz), 5.34 (q, 0.3H, J=7.1 Hz), 5.82 (q, 0.7H, J=6.9Hz), 7.20-7.30 (m, 1H), 7.35-7.44 (m,1H); LC/MS 422 (M+1); Compound fromthe slower eluting diastereomer: ¹H NMR (500 MHz, CD₃OD) δ1.54 (d, 2.1H,J=6.8 Hz), 1.66 (d, 0.9H, J=6.9 Hz), 2.70-3.16 (m, 4H), 3.40-3.46 (m,0.3H), 3.75-3.98 (m, 1.7H), 4.13 (dt, 0.3H, J=4.1, 11.9 Hz), 4.25-4.42(m, 2.4H), 5.00 (dd, 0.3H, J=4.1, 14.0 Hz), 5.33 (q, 0.3H, J=7.1 Hz),5.84 (q, 0.7H, J=6.9 Hz), 7.20-7.30 (m, 1H), 7.35-7.45 (m, 1H); LC/MS422 (M+1).

EXAMPLE 3

[7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol,hydrochloride Step A:[7-N-(tert-Butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol

To a solution of 1.86 g (6.38 mmol) of7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(Ex. 2, Step A) in 20 mL of toluene at −78° C. was added 5.88 mL (7.65mmol, 1.3 M solution in cyclohexane) of sec-butyllithium. The reactionmixture was stirred at −78° C. for 20 min, then 0.524 mL (7.01 mmol) ofcyclopropanecarboxaldehyde was added dropwise. The reaction mixture wasstirred at −78° C. for 10 min. The −78° C. bath was removed and themixture was allowed to stir at ambient temperature for 1 h. The reactionwas quenched by the addition of saturated aqueous ammonium chloridesolution and extracted with three portions of ethyl acetate. Thecombined organic phases were washed with brine, dried over magnesiumsulfate, and concentrated to give 2.24 g of crude material. Purificationby flash chromatography (silica gel, 7 to 10% ethyl acetate/hexane) gavethe title compound as a mixture of 4 diastereomers. LC/MS 363 (M+1).

Step B:[2-(Trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol,hydrochloride

The BOC protecting group was removed from a 400 mg portion of7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanolessentially following the procedure outlined in Example 2, Step C toprovide the title compound. LC/MS 245 (M+1-H₂O).

Step C:[7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol

A 160 mg portion of[2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanolhydrochloride was coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step D.Purification by preparative TCL (silica gel, 10%methanol/dichloromethane) gave 176 mg of the product as a mixture ofdiastereomers. HPLC (OD chiralcel column, 6% ethanol/hexane) separatedthe first and last eluting diastereomers. The middle fractionscontaining two diastereomers were further subjected to HPLC (ODchiralcel column, 3% ethanol/hexane) to provide the second and the thirdeluting diastereomers. LC/MS 504 (M+1-tBu-H₂O).

Step D:[7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanolhydrochloride

The BOC protecting group was removed from a 12 mg portion of[7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol(second eluting diastereomer) essentially following the procedureoutlined in Example 2, Step E to provide the title compound as a singlediastereomer of unknown configuration. LC/MS 478 (M+1). The otherisomers were deprotected in a similar manner.

EXAMPLE 4

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[15-α]pyrazine, hydrochloride Step A:7-N-(tert-Butoxycarbonyl)-8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

A solution of 200 mg (0.55 mmol) of[7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol(prepared as outlined in Example 3, Step A) in 3.5 mL of dichloromethanewas cooled to −78° C. and 0.406 mL (3.31 mmol) of (diethylamino)sulfurtrifluoride (DAST) was added. The reaction mixture was stirred at −78°C. for 1 h, then warmed to ambient temperature and stirred overnight.The reaction mixture was partitioned between saturated aqueous sodiumbicarbonate solution and dichloromethane. The aqueous phase wasextracted with three portions of dichloromethane. The combined organicphases were washed with brine, dried over magnesium sulfate, andconcentrated. Purification by HPLC (Gilson, YMC C-18, 10 to 90%acetonitrile/water gradient) gave the title compound. LC/MS 289(M+1-tBu-HF).

Step B:8-[Cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride

The BOC protecting group was removed from a 100 mg portion of7-N-(tert-butoxycarbonyl)-8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazineessentially following the procedure outlined in Example 2, Step C toprovide the title compound. LC/MS 265 (M+1).

Step C:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

A 90 mg portion of8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride was coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step Dwith the exception that the reaction mixture was stirred for 3 days.Purification by HPLC (OD chiralcel column, 7% ethanol/hexane) gave 1.8mg of the first eluting diastereomer, 22.7 mg of the second, 7.4 mg ofthe third, and 24.4 mg of the fourth eluting diastereomer. LC/MS 480(M+1-BOC).

Step D:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride

The BOC protecting group was removed from a 24 mg portion of7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-[cyclopropyl(fluoro)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(fourth eluting diastereomer from Step C) essentially following theprocedure outlined in Example 2, Step E to provide the title compound asa single diastereomer of unknown configuration. LC/MS 480 (M+1). Theother isomers were deprotected in a similar manner.

EXAMPLE 5

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride Step A: tert-Butyl8-(cyclopropylmethylene)-2-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[1,5-α]pyrazine-7(8H)-carboxylate

A solution of 100 mg (0.28 mmol) of[7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazin-8-yl](cyclopropyl)methanol (prepared asoutlined in Example 3, Step A), 52.4 mg (0.294 mmol) of1,1-thiocarbonyldiimidazole, and 3.4 mg (0.028 mmol) of4-(dimethylamino)pyridine in 2.0 mL of dichloroethane was stirred atreflux temperature for 17 h. The reaction mixture was cooled to ambienttemperature and concentrated in vacuo. The residue was partitionedbetween saturated aqueous sodium bicarbonate solution and ethyl acetate.The aqueous phase was extracted with three portions of ethyl acetate.The combined organics were washed with brine, dried over magnesiumsulfate and concentrated. Purification by preparative TLC (silica gel)gave the title compound as a clear semi-solid. LC/MS 289 (M+1-tBu).

Step B:7-N-(tert-Butoxycarbonyl)-8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

A mixture of 50 mg (0.15 mmol) of tert-butyl8-(cyclopropylmethylene)-2-(trifluoromethyl)-5,6-dihydro[1,2,4]triazolo[1,5-α]pyrazine-7(8H)-carboxylateand 25 mg of 10% palladium on carbon in 0.5 mL of ethanol was stirredunder an atmosphere of hydrogen overnight. The mixture was filtered andthe filtrate concentrated to give the title compound. LC/MS 291(M+1-tBu).

Step C:8-(Cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride

The BOC protecting group was removed from a 42 mg portion of7-N-(tert-butoxycarbonyl)-8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro1,2,4]triazolo[1,5-α]pyrazine essentially following the procedureoutlined in Example 2, Step C to provide the title compound. LC/MS 247(M+1).

Step D:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

A 35 mg portion of8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride was coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step D,with the following exception. The reaction mixture was stirred atambient temperature for 24 h and then concentrated. The residue waspurified by preparative TLC (silica gel, 10% methanol/dichloromethane)to provide 54 mg of the title compound as a mixture of diastereomers.The diastereomers were separated by HPLC (OD chiralcel column, 7%ethanol/hexane) to give the faster eluting diastereomer and the slowereluting diastereomer. LC/MS 462 (M+1-BOC).

Step E:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride

The BOC protecting group was removed from a 12 mg portion of7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-(cyclopropylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(slower eluting diastereomer from Step C) essentially following theprocedure outlined in Example 2, Step E to provide the title compound asa single diastereomer of unknown configuration. LC/MS 462 (M+1). Theother isomer was deprotected in a similar manner.

EXAMPLE 6

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-cyclopropyl-56,7,8-tetrahydro[1,2,4]triazolo[1 5-α]pyrazine, hydrochloride Step A:N-Pyrazin-2-ylcyclopropanecarboxamide

To a solution of 10 g (105 mmol) of 2-aminopyrazine in 100 mL ofpyridine was added dropwise a solution of 10.99 g (9.56 mL, 105 mmol) ofcyclopropanecarbonyl chloride in 100 mL of dichloromethane. Theresultant yellow solution was stirred at ambient temperature for 2 h.The reaction mixture was concentrated in vacuo. The residue wasdissolved in ethyl acetate and a small amount of water and washedsequentially with 1 M aqueous cuprous sulfate solution and water. Thewater layer was extracted with three portions of ethyl acetate. Thecombined organic phases were washed with brine, dried over magnesiumsulfate, and concentrated. Purification by flash chromatography (silicagel, eluting sequentially with 50%, 80% and 100% ethyl acetate/hexane)gave the title compound. LC/MS 164 (M+1).

Step B: 1-Amino-2-[(cyclopropylcarbonyl)amino]pyrazin-1-ium2,4,6-trimethylbenzenesulfonate

To a solution of 1.0 g (6.13 mmol) ofN-pyrazin-2-ylcyclopropanecarboxamide in 10 mL of dichloromethane at 0°C. was added a solution of 1.58 g (7.36 mmol) ofO-mesitylenesulfonylhydroxylamine, prepared from mesitylenesulfonylchloride using a procedure analogous to that described in the literature(Y. Tamura et al., J. Org. Chem., 38: 1239 (1973)). The reaction mixturewas allowed to stir at ambient temperature for 1.5 h. The resultantthick yellow mixture was concentrated in vacuo to give the titlecompound as a yellow solid. LC/MS 179 (M).

Step C: 2-Cyclopropyl[1,2,4]triazolo[1,5-α]pyrazine

1-Amino-2-[(cyclopropylcarbonyl)amino]pyrazin-1-ium2,4,6-trimethylbenzene-sulfonate (2.6 g) was cyclized usingpolyphosphoric acid, essentially following the procedure outlined inExample 1, Step C, except that the mixture was heated at 130° C.Purification by HPLC (Gilson, YMC C-18 column, 90 to 10%water/acetonitrile gradient) gave the title compound. LC/MS 161 (M+1).

Step D: 2-Cyclopropyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride

A mixture of 158 mg (0.15 mmol) of2-cyclopropyl[1,2,4]triazolo[1,5-α]pyrazine and 100 mg of 10% palladiumon carbon in ethanol (5 mL) was stirred under an atmosphere of hydrogenfor 3 h. The mixture was filtered and the filtrate was concentrated togive the free base of the title compound as a yellowish solid. LC/MS 165(M+1).

In order to further purify this compound, 140 mg (0.854 mmol) wasconverted to its BOC derivative essentially following the procedureoutlined in Example 2, Step A, except that no extractive work-up wasperformed. After evaporation of solvent, the residue was purified byflash chromatography (silica gel, eluting with a 10% to 60% ethylacetate/hexane gradient) to give 62 mg of7-N-(tert-butoxycarbonyl)-2-cyclopropyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine.LS/MS 209 (M+1-tBu). The BOC group was removed according to theprocedure outlined in Example 2, Step C to give the title compound.LC/MS 165 (M+1).

Step E:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-cyclopropyl-5,6,7,8-tetrahydro[12,4triazolo[4,3-α]pyrazine

A 54 mg portion of2-cyclopropyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinehydrochloride was coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step D.Purification by two sequential preparative TLC columns (silica gel, 10%methanol/dichloromethane) gave the title compound as a white solid.LC/MS 380 (M+1-BOC).

Step F:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-cyclopropyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride

The BOC protecting group was removed from a 42 mg portion of7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-cyclopropyl-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazineessentially following the procedure outlined in Example 2, Step E toprovide the title compound as a white solid. LC/MS 380 (M+1).

EXAMPLE 7

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-([1,2,4]triazol-4-ylmethyl)-2-trifluoromethyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride Step A:7-N-(tert-Butoxycarbonyl)-8-[(benzyloxy)methyl]-2-(trifluoromethyl)-5,6,7,8tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

The title compound was prepared from 2.06 g (7.06 mmol) of7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(Example 2, Step A) and benzyl chloromethyl ether essentially followingthe procedure outlined in Example 2, Step B. Purification by flashchromatography (silica gel, 5 to 10% ethyl acetate/hexane gradient) gavethe title compound as a white foam. LC/MS 357 (M+1-tBu).

Step B:7-N-(tert-Butoxycarbonyl)-8-(hydroxymethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a solution of 733 mg (1.8 mmol) of7-N-(tert-butoxycarbonyl)-8-[(benzyloxy)methyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinein 8.0 mL of ethanol was added 400 mg of 10% palladium on carbon. Themixture was stirred under an atmosphere of hydrogen for 29 h. TLCanalysis indicated that starting material was present. Thus 400 mg of10% palladium on carbon was added and the mixture shaken on a Parrapparatus under 42 psi hydrogen for 12 h. The reaction mixture wasfiltered through Celite and concentrated. Flash chromatography (silicagel, 7% to 50% ethyl acetate/hexane gradient) gave the title compound asa white solid. LC/MS 267 (M+1-tBu).

Step C:7-N-(tert-Butoxycarbonyl)-8-(methanesulfonyloxymethyl)-2-(trifluoromethyl)5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a 0° C. solution of 100 mg (0.31 mmol) of7-N-(tert-butoxycarbonyl)-8-(hydroxymethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinein 1.0 mL of dichloromethane was added sequentially 0.047 mL (0.341mmol) of triethylamine and 0.029 mL (0.372 mmol) of methanesulfonylchloride. The reaction mixture was stirred at 0° C. and allowed to warmto room temperature for 4 h. Aqueous sodium bicarbonate solution wasadded, and the resultant mixture was extracted with three portions ofdichloromethane. The combined organics were washed with brine, driedover magnesium sulfate, and concentrated to give a yellow oil which wasused without further purification. LC/MS 401 (M+1).

Step D:7-N-(tert-Butoxycarbonyl)-8-([1,2,4]triazol-4-ylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a solution of 47 mg (0.683 mmol) of [1,2,4]triazole in 1.0 mL of DMFwas added 189 mg (1.365 mmol) of potassium carbonate. The mixture washeated at 50° C. for 15 min. To this was added 182 mg (0.455 mmol) of7-N-(tert-butoxycarbonyl)-8-(methanesulfonyloxymethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine.The mixture was stirred at 50° C. for 14 h. DMF was removed in vacuo andthe residue was partitioned between ethyl acetate and water. The aqueousphase was extracted with three portions of ethyl acetate. The combinedorganics were dried over magnesium sulfate and concentrated to give 107mg of an orange oil. The mixture was eluted on a preparative TLC plate(silica gel, 50% ethyl acetate/hexane). The plate was scraped and theproduct eluted from the silica gel with 80:15:1chloroform/methanol/ammonium hydroxide to give the title compound. LC/MS318 (M+1-tBu).

Step E:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-([1,2,4]triazol-4-ylmethyl)-2-trifluoromethyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

Essentially following the procedures outlined in Example 2, Steps C, Dand E, the title compound as a mixture of diastereomers was preparedfrom 69.2 mg of7-N-(tert-butoxycarbonyl)-8-([1,2,4]triazol-4-ylmethyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine.LC/MS 489 (M+1).

EXAMPLE 8

7-F(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-(carboxymethyl)-2-trifluoromethyl-5,6,7,8-tetrahydro[1,2,4]triazolo[15-α]pyrazine,trifluoroacetic acid salt Step A:7-N-(tert-Butoxycarbonyl)-8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}-2-(trifluoromethyl)-5,6,78-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a solution of 1.40 g (4.79 mmol) of7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(Example 2, Step A) in 20 mL of toluene at −78° C. was addedN,N,N,N-tetramethylethylenediamine (0.760 mL, 5.03 mmol) followed byn-butyllithium (2.01 mL of a 2.5M solution in hexanes, 5.03 mmol). Themixture was stirred at −78° C. for 10 min and then benzyl-2-bromoacetate(0.790 mL, 5.03 mmol) was added dropwise. The mixture was allowed tostir at −78° C. for 10 min, and then it was warmed to ambienttemperature. The reaction was quenched with aqueous ammonium chloridesolution, and the aqueous layer was extracted three times with ethylacetate. The combined organic layers were washed with brine, dried overmagnesium sulfate, and concentrated. Purification by flashchromatography (silica gel, 2 to 15% ethyl acetate/hexane gradient), andfurther reverse phase purification (Gilson, YMC C-18, 10 to 90%acetonitrile/water gradient) yielded the title compound. LC/MS 441(M+1).

Step B:8-{2-Oxo-2-[(phenylmethyl)oxy]ethyl}-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,trifluoroacetic acid salt

To a solution of7-N-(tert-butoxycarbonyl)-8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(0.240 g, 0.545 mmol) in 2.0 mL of dichloromethane was added 2.0 mLtrifluoroacetic acid. The reaction was stirred at ambient temperaturefor 18 h. Concentration in vacuo gave the title compound. LC/MS 341(M+1).

Step C:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine

A 282 mg portion of8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,trifluoroacetic acid salt was coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step Dwith stirring for 72 h. Purification by preparative TLC (silica gel, 10%methanol/dichloromethane) followed by HPLC (OD chiralcel column, 15%isopropanol/heptane) separated the first and last eluting diastereomers.LC/MS 656 (M+1).

Step D:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine,trifluoroacetic acid salt

To a solution of 19.7 mg (0.030 mmol) of the slower eluting diastereomerof7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazinefrom Step C in 1 mL of dichloromethane was added 1 mL of trifluoroaceticacid. After 3 h, the reaction was concentrated in vacuo to give thetitle compound as clear viscous material. LC/MS 556 (M+1).

In a separate experiment, to a solution of 17.4 mg of the faster elutingdiastereomer in 1 mL of dichloromethane was added 1 mL oftrifluoroacetic acid. The reaction was stirred at ambient temperaturefor 3h. Concentration gave the product as clear viscous material. LC/MS556 (M+1).

Step E:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-(carboxymethyl)-2-trifluoromethyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,trifluoroacetic acid salt

The deprotected faster eluting diastereomer of7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-{2-oxo-2-[(phenylmethyl)oxy]ethyl}-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine(8.0 mg, 0.014 mmol, from Step D) was hydrogenated under 42 psi hydrogenwith 10% palladium on carbon (5.0 mg) as a catalyst in methanol (1.5 mL)at ambient temperature for 18 h. Filtration through Celite followed byconcentration gave the title compound as a clear viscous oil. LC/MS 466(M+1).

In a separate experiment, the deprotected slower eluting diastereomer(5.0 mg, 0.0090 mmol, from Step D) was hydrogenated under 42 psihydrogen with 10% palladium on carbon (2.0 mg) as a catalyst in methanol(1.5 mL) at ambient temperature for 18 h. Filtration through Celitefollowed by concentration gave the title compound as a clear viscousoil. LC/MS 466 (M+1).

EXAMPLE 9

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-[[(dimethylamino)carbonyl]methyl]-2-trifluoromethyl-56,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine, hydrochloride Step A:2-Bromo-N,N-dimethylacetamide

To a solution of bromoacetyl bromide (13.01 g, 64.46 mmol) indichloromethane (100 mL) was added triethylamine (18.9 mL, 135.4 mmol)dropwise at −78° C. The reaction mixture was stirred at −78° C. for 10min and at ambient temperature for 1 h, then washed with saturatedaqueous sodium bicarbonate solution followed by 2N hydrochloric acid.The organic phase was washed with brine and dried over anhydrousmagnesium sulfate. Concentration followed by flash chromatography (50%ethyl acetate/hexanes, then 100% ethyl acetate) afforded the titlecompound as an oil. LC/MS 165.8 (M+1), 167.8 (M+3).

Step B:7-N-(tert-Butoxycarbonyl)-8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

To a solution of 2.13 g (7.30 mmol) of7-N-(tert-butoxycarbonyl)-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(Example 2, Step A) in 10 mL of tetrahydrofuran at −78° C. was addedlithium diisopropylamide (4.02 mL of a 2.0M solution inheptane/tetrahydrofuran/ethylbenzene, 8.03 mmol). The mixture wasallowed to stir at −78° C. for 15 min, and then2-bromo-N,N-dimethylacetamide from Step A in 5 mL of tetrahydrofuran wasadded, and the mixture slowly warmed to ambient temperature over 18 h.The reaction was quenched with aqueous ammonium chloride and the aqueouslayer was extracted three times with ethyl acetate. The combined organiclayers were washed with brine, dried over magnesium sulfate, andconcentrated. Purification by flash chromatography (silica gel, gradientof 50% to 75% ethyl acetate/hexane) yielded the title compound. LC/MS322 ((M+1)-t-butyl).

Step C:8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride

7-N-(tert-butoxycarbonyl)-8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine(630 mg, 1.67 mmol) was dissolved in 5 mL of methanol saturated withhydrogen chloride. The reaction was stirred at ambient temperature for 1h. Concentration in vacuo gave the title compound as an off-white solid.LC/MS 278 (M+1).

Step D:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine

A 200 mg portion of8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride was coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step D.Purification by preparative TLC (silica gel, 10%methanol/dichloromethane) followed by HPLC (AD chiral pak column, 15%isopropanol/heptane) separated the first and last eluting diastereomers.LC/MS 593 (M+1).

Step E:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4triazolo[4,3-α]pyrazine,hydrochloride

To 57.7 mg (0.097 mmol) of the slower eluting diastereomer of7-[(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-8-[2-(dimethylamino)-2-oxoethyl]-2-(trifluoromethyl)-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-α]pyrazinefrom Step D was added 1 mL of methanol saturated with hydrochloric acid.After 1 h, the reaction was concentrated in vacuo to give the titlecompound as a white solid. LC/MS 493 (M+1).

In a separate experiment, to 83 mg of the faster eluting diastereomerwas added 1 mL of methanol saturated with hydrochloric acid. Thereaction was stirred at ambient temperature for 1 h. Concentration gavethe product as a white solid. LC/MS 493 (M+1).

EXAMPLE 10

7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-5,8-dimethyl-2-difluoromethyl-5,6,7,8-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine,hydrochloride Step A: 3-Hydrazino-2,5-dimethylpyrazine

To 3-chloro-2,5-dimethylpyrazine (26.0 g, 0.182 mol) placed in a roundbottom flask was added hydrazine hydrate (75 mL). The reaction mixturewas refluxed for 3 h, cooled to ambient temperature, and then kept in arefrigerator for 24 h. The precipitate was collected and washed withhexanes and diethyl ether to afford the title compound as dark coloredsolid. The compound was used in the next step without furtherpurification. LC/MS 138.9 (M+1); ¹H-NMR (500 MHz, CDCl₃): δ 2.33 (s,3H), 2.41 (s, 3H), 4.10 (br S, 2H), 5.75 (br s, 1H), 7.70 (s, 1H).

Step B: 3,6-Dimethylpyrazin-2-amine

To a solution of 3-hydrazino-2,5-dimethylpyrazine (2.00 g, 14.5 mmol)from Step A in 75 mL of water was added approximately 1 g (wet) RaneyNi, 50% slurry in water. After stirring at reflux for 2 h, the reactionmixture was filtered hot through Celite, and subsequently washed withhot water, followed by dichloromethane. The concentrated residues weresuspended in ethylenediamine and heated at 50° C. for 30 min withstirring. Concentration followed by purification by flash chromatography(silica gel, 50% ethyl acetate/hexane) yielded the title compound. LC/MS124 (M+1).

Step C: 2,2-Difluoro-N-(3,6-dimethylpyrazin-2-yl)acetamide

To a slightly heterogeneous solution of 3,6-dimethylpyrazin-2-amine(1.88 g, 15.3 mmol) and N,N-diisopropylethylamine (5.32 mL, 30.5 mmol)in dichloromethane (75 mL) was added difluoroacetic anhydride (3.19 g,18.3 mmol) dropwise at 0° C. The solution was stirred at 0° C. for 10min and at ambient temperature for 2 h. The mixture was partitionedbetween dichloromethane and brine. The aqueous portion was extractedwith dichloromethane, washed with brine, and dried over anhydrousmagnesium sulfate. Concentration gave the title compound as a brownsolid. LC/MS 202 (M+1).

Step D:2,2-Difluoro-N′-hydroxy-N-(3,6-dimethylpyrazin-2-yl)ethanimidamide

To a suspension of 2,2-difluoro-N-(3,6-dimethylpyrazin-2-yl)acetamide(4.65 g, 23.1 mmol, from Step C) in 1,2-dichloroethane (55 mL) was addedphosphorous pentachloride (7.23 g, 34.7 mmol) portionwise. The mixturewas refluxed for 20 h. After evaporation of dichloroethane, the residuewas suspended in tetrahydrofuran (55 mL). To the above mixture was added50% aqueous hydroxylamine (5 m]L) dropwise. After stirring at ambienttemperature for 1 h, the mixture was partitioned between ethyl acetateand aqueous sodium bicarbonate. The aqueous layer was extracted threetimes with ethyl acetate. The combined organic layers were washed withbrine and dried over anhydrous magnesium sulfate. Concentration gave thetitle compound as a yellow solid. LC/MS 217 (M+1).

Step E: 2-(Difluoromethyl)-5,8-dimethyl[1,2,4]triazolo[1,5-α]pyrazine

A mixture of2,2-difluoro-N′-hydroxy-N-(3,6-dimethylpyrazin-2-yl)ethanimidamide (3.05g, 14.1 mmol, from Step D) and superphosphoric acid (100 mL) was heatedto 130° C. with stirring for 18 h. The solution was added to ice andneutralized by addition of ammonium hydroxide. The dark aqueous solutionwas extracted three times with ethyl acetate, washed with brine, anddried over anhydrous magnesium sulfate. Concentration followed by flashchromatography (35% ethyl acetate/hexane) afforded the title compound asa yellow solid. LC/MS 199 (M+1).

Step F:2-(Difluoromethyl)-5,8-dimethyl[5,6,7,8]-tetrahydro[1,2,4]triazolo[1,5-α]pyrazine

2-(Difluoromethyl)-5,8-dimethyl[1,2,4]triazolo[1,5-α]pyrazine (1.65 g,8.33 mmol, from Step E) was hydrogenated under atmospheric hydrogen with10% palladium on carbon (300 mg) as a catalyst in ethanol (30 mL) atambient temperature for 18 h. As indicated by TLC, only startingmaterial was present. After the addition of 10% palladium on carbon (500mg), the reaction was placed on the Parr Hydrogenator under 42 psi ofhydrogen with mixing for 63 h. Filtration through Celite followed byconcentration gave the title compound. LC/MS 203 (M+1).

Step G:7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-(difluoromethyl)-5,8-dimethyl[5,6,7,8]-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine

A 200-mg portion of2-(difluoromethyl)-5,8-dimethyl[5,6,7,8]-tetrahydro[1,2,4]triazolo[1,5-α]pyrazinewas coupled to(3R)-3-[(tert-butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoicacid essentially following the procedure outlined in Example 2, Step Dwith heating at 60° C. Purification by preparative TLC (silica gel, 10%methanol/dichloromethane) followed by HPLC (OD chiral pak column, 12%isopropanol/heptane) separated the first and last eluting diastereomers.LC/MS 418 (M+1-Boc).

Step H:7-[(3R)-3-Amino-4-(2,4,5-trifluorophenyl)butanoyl]-2-(difluoromethyl)-5,8-dimethyl[5,6,7,8]-tetrahydro[1,2,4]triazolo[4,3-α]pyrazine,hydrochloride

To 81.0 mg (0.157 mmol) of the slower eluting diastereomer of7-[(3R)-3-[(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoyl]-2-(difluoromethyl)-5,8-dimethyl[5,6,7,8]-tetrahydro[1,2,4]triazolo[4,3-α]pyrazinefrom Step G was added 2 mL of methanol saturated with hydrochloric acid.After 1 h, the reaction was concentrated in vacuo to give the titlecompound as a white solid. LC/MS 418 (M+1).

In a separate experiment, to 54.1 mg of the faster eluting diastereomerwas added 2 mL of methanol saturated with hydrochloric acid. Thereaction was stirred at ambient temperature for 1 h. Concentration gavethe product as a white solid. LC/MS 418 (M+1).

Essentially following the procedures outlined for Examples 1-10, thecompounds listed in Table 2 were prepared. TABLE 2

MS Example R³ R⁸ R¹ (M + 1) 11 2-F,5-F H CF₃ 390 12 2-F,4-F,5-FCH₂(4-CF₃—Ph) CF₃ 566 13 2-F,4-F,5-F CH₂(4-F—Ph) CF₃ 516 14 3-F,4-FCH₂(4-F—Ph) CF₃ 498 15 3-F,4-F CHOH(cPr) CF₃ 460 16 2-F,4-F,5-F H CF₃340 17 2-F,4-F,5-F CH₂OCH₂Ph CF₃ 528 18 3-F,4-F CH₂(1,2,4- CF₃ 471triazol-1-yl) 19 2-F,4-F,5-F CH₂(imidazol- CF₃ 488 1-yl) 20 2-F,4-F,5-FCH₂(pyrazol-1- CF₃ 488 yl) 21 2-F,5-F Me CF₃ 404 22 2-F,4-F,5-FCH₂CO₂CH₂Ph CF₃ 556 23 2-F,4-F,5-F H CHF₂ 390 24 2-F,4-F,5-F Me CHF₂ 40425 2-F,4-F,5-F CH₂OMe CF₃ 452

Example of a Pharmaceutical Formulation

As a specific embodiment of an oral pharmaceutical composition, a 100 mgpotency tablet is composed of 100 mg of any of the compounds of thepresent invention, 268 mg microcrystalline cellulose, 20 mg ofcroscarmellose sodium, and 4 mg of magnesium stearate. The active,microcrystalline cellulose, and croscarmellose are blended first. Themixture is then lubricated by magnesium stearate and pressed intotablets.

While the invention has been described and illustrated with reference tocertain particular embodiments thereof, those skilled in the art willappreciate that various adaptations, changes, modifications,substitutions, deletions, or additions of procedures and protocols maybe made without departing from the spirit and scope of the invention.For example, effective dosages other than the particular dosages as setforth herein above may be applicable as a consequence of variations inresponsiveness of the mammal being treated for any of the indicationswith the compounds of the invention indicated above. The specificpharmacological responses observed may vary according to and dependingupon the particular active compounds selected or whether there arepresent pharmaceutical carriers, as well as the type of formulation andmode of administration employed, and such expected variations ordifferences in the results are contemplated in accordance with theobjects and practices of the present invention. It is intended,therefore, that the invention be defined by the scope of the claimswhich follow and that such claims be interpreted as broadly as isreasonable.

1. A compound of the formula I:

or a pharmaceutically acceptable salt thereof; wherein each n isindependently 0, 1, or 2; X is N or CR²; Ar is phenyl substituted withone to five R³ substituents; R¹ and R² are each independently selectedfrom the group consisting of hydrogen, halogen, cyano, C₁₋₁₀ alkyl,wherein alkyl is unsubstituted or substituted with one to five halogens,C₁₋₁₀ alkoxy, wherein alkoxy is unsubstituted or substituted with one tofive substituents independently selected from halogen or hydroxy, C₁₋₁₀alkylthio, wherein alkylthio is unsubstituted or substituted with one tofive substituents independently selected from halogen or hydroxy, C₂₋₁₀alkenyl, wherein alkenyl is unsubstituted or substituted with one tofive substituents independently selected from halogen or hydroxy,(CH₂)_(n)COOH, (CH₂)_(n)COOC₁₋₆ alkyl, (CH₂)_(n)CONR⁴R⁵, wherein R⁴ andR⁵ are independently selected from the group consisting of hydrogen,tetrazolyl, thiazolyl, (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆ cycloalkyl, andC₁₋₆ alkyl, wherein alkyl is unsubstituted or substituted with one tofive halogens and wherein phenyl and cycloalkyl are unsubstituted orsubstituted with one to five substituents independently selected fromhalogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxyare unsubstituted or substituted with one to five halogens; or R⁴ and R⁵together with the nitrogen atom to which they are attached form aheterocyclic ring selected from azetidine, pyrrolidine, piperidine,piperazine, and morpholine wherein said heterocyclic ring isunsubstituted or substituted with one to five substituents independentlyselected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, whereinalkyl and alkoxy are unsubstituted or substituted with one to fivehalogens; (CH₂)_(n)—NR⁴R⁵, (CH₂)_(n)—OCONR⁴R⁵, (CH₂)_(n)—SO₂NR⁴R⁵,(CH₂)_(n)—SO₂R⁶, (CH₂)_(n)—NR⁷SO₂R⁶, (CH₂)_(n)—NR⁷CONR⁴R⁵,(CH₂)_(n)—NR⁷COR⁷, (CH₂)_(n)—NR⁷CO₂R⁶, (CH₂)_(n)—COR⁶, (CH₂)_(n)-aryl,wherein aryl is unsubstituted or substituted with one to fivesubstituents independently selected from halogen, CN, hydroxy, NR⁷SO₂R⁶,SO₂R⁶, CO₂H, C₁₋₆ alkyloxycarbonyl, C₁₋₆ alkyl and C₁₋₆ alkoxy, whereinalkyl and alkoxy are unsubstituted or substituted with one to fivesubstituents independently selected from halogen, CO₂H, and C₁₋₆alkyloxycarbonyl, (CH₂)_(n)-heteroaryl, wherein heteroaryl isunsubstituted or substituted with one to three substituentsindependently selected from hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens, (CH₂)_(n)-heterocyclyl, wherein heterocyclyl isunsubstituted or substituted with one to three substituentsindependently selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens, (CH₂)_(n)—C₃₋₆ cycloalkyl, wherein cycloalkyl isunsubstituted or substituted with one to three substituentsindependently selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens; and wherein any methylene (CH₂) carbon atom in R¹or R² is unsubstituted or substituted with one to two groupsindependently selected from halogen, hydroxy, and C₁₋₄ alkylunsubstituted or substituted with one to five halogens; each R³ isindependently selected from the group consisting of hydrogen, halogen,cyano, hydroxy, C₁₋₆ alkyl, unsubstituted or substituted with one tofive halogens, and C₁₋₆ alkoxy, unsubstituted or substituted with one tofive halogens; R⁶ is independently selected from the group consisting oftetrazolyl, thiazolyl, (CH₂)_(n)-phenyl, (CH₂)_(n)-C₃₋₆ cycloalkyl, andC₁₋₆ alkyl, wherein alkyl is unsubstituted or substituted with one tofive halogens and wherein phenyl and cycloalkyl are unsubstituted orsubstituted with one to five substituents independently selected fromhalogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxyare unsubstituted or substituted with one to five halogens, and whereinany methylene (CH₂) carbon atom in R⁶ is unsubstituted or substitutedwith one to two groups independently selected from halogen, hydroxy,C₁₋₄ alkyl, and C₁₋₄ alkoxy, wherein alkyl and alkoxy are unsubstitutedor substituted with one to five halogens; each R⁷ is hydrogen or R⁶; R⁸,R⁹, R¹⁰, R¹¹, R¹², and R¹³ are each independently selected from thegroup consisting of: hydrogen, cyano, (CH₂)_(n)COOH, (CH₂)_(n)COOC₁₋₆alkyl, wherein alkyl is unsubstituted or substituted with one to threesubstituents independently selected from halogen and phenyl, C₁₋₁₀alkyl, unsubstituted or substituted with one to five substituentsindependently selected from halogen, hydroxy, C₁₋₆ alkoxy, carboxy, C₁₋₆alkyloxycarbonyl, and phenyl-C₁₋₁₃ alkoxy, wherein alkoxy isunsubstituted or substituted with one to five halogens, (CH₂)_(n)-aryl,wherein aryl is unsubstituted or substituted with one to fivesubstituents independently selected from halogen, hydroxy, C₁₋₆ alkyl,and C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted orsubstituted with one to five halogens, (CH₂)_(n)-heteroaryl, whereinheteroaryl is unsubstituted or substituted with one to threesubstituents independently selected from hydroxy, halogen, C₁₋₆ alkyl,and C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted orsubstituted with one to five halogens, (CH₂)_(n)-heterocyclyl, whereinheterocyclyl is unsubstituted or substituted with one to threesubstituents independently selected from oxo, hydroxy, halogen, C₁₋₆alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted orsubstituted with one to five halogens, (CH₂)_(n)—C₃₋₆ cycloalkyl,wherein cycloalkyl is unsubstituted or substituted with one to threesubstituents independently selected from halogen, hydroxy, C₁₋₆ alkyl,and C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted orsubstituted with one to five halogens, (CH₂)_(n)CONR⁴R⁵, wherein R⁴ andR⁵ are independently selected from the group consisting of hydrogen,tetrazolyl, thiazolyl, (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆ cycloalkyl, andC₁₋₆ alkyl, wherein alkyl is unsubstituted or substituted with one tofive halogens and wherein phenyl and cycloalkyl are unsubstituted orsubstituted with one to five substituents independently selected fromhalogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxyare unsubstituted or substituted with one to five halogens; or whereinR⁴ and R⁵ together with the nitrogen atom to which they are attachedform a heterocyclic ring selected from azetidine, pyrrolidine,piperidine, piperazine and morpholine wherein said heterocyclic ring isunsubstituted or substituted with one to five substituents independentlyselected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, whereinalkyl and alkoxy are unsubstituted or substituted with one to fivehalogens; and wherein any methylene (CH₂) carbon atom in R⁸, R⁹, R¹⁰,R¹¹, R¹², or R¹³ is unsubstituted or substituted with one to two groupsindependently selected from halogen, hydroxy, and C₁₋₄ alkylunsubstituted or substituted with one to five halogens.
 2. The compoundof claim 1 of the formula Ia:

wherein the carbon atom marked with an * has the R configuration and Ar,X, R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined in claim
 1. 3. Thecompound of claim 1 of the formula Ib:

wherein Ar, R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined inclaim
 1. 4. The compound of claim 3 of the formula Ic:

wherein the carbon atom marked with an * has the R configuration and Ar,R¹, R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined in claim
 1. 5. Thecompound of claim 3 of the formula Id:

wherein Ar, R¹, and R⁸ are as defined in claim
 1. 6. The compound ofclaim 1 of the formula Ie:

wherein Ar, R¹, R², R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined inclaim
 1. 7. The compound of claim 6 of the formula If:

wherein the carbon atom marked with an * has the R configuration and Ar,R¹, R², R⁸, R⁹, R¹⁰, R¹¹, R¹², and R¹³ are as defined in claim
 1. 8. Thecompound of claim 6 of the formula Ig:

wherein Ar, R¹, R², and R⁸ are as defined in claim
 1. 9. The compound ofclaim 1 wherein R³ is selected from the group consisting of hydrogen,fluoro, chloro, bromo, trifluoromethyl, and methyl.
 10. The compound ofclaim 9 wherein R³ is selected from the group consisting of hydrogen,fluoro, and chloro.
 11. The compound of claim 10 wherein R³ is hydrogenor fluoro.
 12. The compound of claim 1 wherein R¹ is selected from thegroup consisting of: hydrogen, C₁₋₆ alkyl, wherein alkyl isunsubstituted or substituted with one to five fluorines,(CH₂)_(n)-phenyl wherein phenyl is unsubstituted or substituted with oneto five substituents independently selected from hydroxy, halogen, C₁₋₆alkyl, C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted orsubstituted with one to five halogens, C₃₋₆ cycloalkyl, unsubstituted orsubstituted with one to five substituents independently selected fromhalogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxyare unsubstituted or substituted with one to five halogens; and whereinany methylene (CH₂) carbon atom in R¹ is unsubstituted or substitutedwith one to two groups independently selected from halogen, hydroxy, andC₁₋₄ alkyl unsubstituted or substituted with one to five halogens. 13.The compound of claim 12 wherein R¹ is selected from the groupconsisting of hydrogen, methyl, ethyl, difluoromethyl, trifluoromethyl,CH₂CF₃, CF₂CF₃, phenyl, and cyclopropyl.
 14. The compound of claim 13wherein R¹ is selected from the group consisting of hydrogen,difluoromethyl, trifluoromethyl, phenyl, and cyclopropyl.
 15. Thecompound of claim 1 wherein R² is selected from the group consisting ofhydrogen, C₁₋₆ alkyl, unsubstituted or substituted with one to fivefluorines, phenyl, unsubstituted or substituted with one to threesubstituents independently selected from fluoro, chloro,trifluoromethyl, methoxy, and OCF₃, and C₃₋₆ cycloalkyl, unsubstitutedor substituted with one to five substituents independently selected fromhalogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxyare unsubstituted or substituted with one to five halogens.
 16. Thecompound of claim 15 wherein R² is selected from the group consisting ofhydrogen, trifluoromethyl, phenyl, and cyclopropyl.
 17. The compound ofclaim 16 wherein R² is hydrogen or trifluoromethyl.
 18. The compound ofclaim 1 wherein R¹ ¹, R¹², and R¹³ are each hydrogen and R⁸, R⁹, and R¹⁰are each independently selected from the group consisting of: hydrogen,C₁₋₆ alkyl, unsubstituted or substituted with one to five substituentsindependently selected from halogen, hydroxy, C₁₋₆ alkoxy, andphenyl-C₁₋₃ alkoxy, wherein alkoxy is unsubstituted or substituted withone to five halogens, (CH₂)_(n)COOH, (CH₂)_(n)COOC₁₋₆ alkyl, whereinalkyl is unsubstituted or substituted with one to three substituentsindependently selected from halogen and phenyl, (CH₂)_(n)CONR⁴R⁵,wherein R⁴ and R⁵ are independently selected from the group consistingof hydrogen, tetrazolyl, thiazolyl, (CH₂)_(n)-phenyl, (CH₂)_(n)—C₃₋₆cycloalkyl, and C₁₋₆ alkyl, wherein alkyl is unsubstituted orsubstituted with one to five halogens and wherein phenyl and cycloalkylare unsubstituted or substituted with one to five substituentsindependently selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens; or wherein R⁴ and R⁵ together with the nitrogenatom to which they are attached form a heterocyclic ring selected fromazetidine, pyrrolidine, piperidine, piperazine and morpholine whereinsaid heterocyclic ring is unsubstituted or substituted with one to fivesubstituents independently selected from halogen, hydroxy, C₁₋₆ alkyl,and C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstituted orsubstituted with one to five halogens, (CH₂)_(n)-phenyl, wherein phenylis unsubstituted or substituted with one to five substituentsindependently selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens, (CH₂)_(n)-heteroaryl, wherein heteroaryl isunsubstituted or substituted with one to three substituentsindependently selected from hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens, (CH₂)_(n)-heterocyclyl, wherein heterocyclyl isunsubstituted or substituted with one to three substituentsindependently selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are unsubstituted or substituted withone to five halogens, (CH₂)_(n)—C₃₋₆ cycloalkyl, wherein cycloalkyl isunsubstituted or substituted with one to three substituentsindependently selected from halogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are optionally substituted with one tofive halogens; and wherein any methylene (CH₂) carbon atom in R⁸, R⁹ orR¹⁰ is unsubstituted or substituted with one to two groups independentlyselected from halogen, hydroxy, and C₁₋₄ alkyl unsubstituted orsubstituted with one to five halogens.
 19. The compound of claim 18wherein R⁸, R⁹, and R¹⁰ are each independently selected from the groupconsisting of: hydrogen, C₁₋₃ alkyl, unsubstituted or substituted withone to three substituents independently selected from halogen, hydroxy,C₁₋₆ alkoxy, and phenyl-C₁₋₃ alkoxy, wherein alkoxy is unsubstituted orsubstituted with one to five halogens, (CH₂)_(n)COOH, (CH₂)_(n)COOC₁₋₆alkyl, wherein alkyl is unsubstituted or phenyl, (CH₂)_(n)CONR⁴R⁵,wherein R⁴ and R⁵ are independently selected from the group consistingof hydrogen and C₁₋₆ alkyl, wherein alkyl is unsubstituted orsubstituted with one to five halogens; or wherein R⁴ and R⁵ togetherwith the nitrogen atom to which they are attached form a heterocyclicring selected from azetidine, pyrrolidine, piperidine, piperazine andmorpholine wherein said heterocyclic ring is unsubstituted orsubstituted with one to five substituents independently selected fromhalogen, hydroxy, C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxyare unsubstituted or substituted with one to five halogens,(CH₂)_(n)-phenyl, wherein phenyl is unsubstituted or substituted withone to five substituents independently selected from halogen, hydroxy,C₁₋₆ alkyl, and C₁₋₆ alkoxy, wherein alkyl and alkoxy are unsubstitutedor substituted with one to five halogens, (CH₂)_(n)-heteroaryl, whereinheteroaryl is unsubstituted or substituted with one to threesubstituents independently selected from hydroxy, halogen, C₁₋₆ alkyl,and C₁₋₆ alkoxy, wherein alkyl and alkoxy are optionally substitutedwith one to five halogens, (CH₂)_(n)-heterocyclyl, wherein heterocyclylis unsubstituted or substituted with one to three substituentsindependently selected from oxo, hydroxy, halogen, C₁₋₆ alkyl, and C₁₋₆alkoxy, wherein alkyl and alkoxy are optionally substituted with one tofive halogens, (CH₂)_(n)—C₃₋₆ cyclopropyl; and wherein any methylene(CH₂) carbon atom in R⁸, R⁹ or R¹⁰ is unsubstituted or substituted withone to two groups independently selected from halogen, hydroxy, and C₁₋₄alkyl unsubstituted or substituted with one to five halogens.
 20. Thecompound of claim 19 wherein R⁸, R⁹, and R¹⁰ are each independentlyselected from the group consisting of: hydrogen, CH₃, CH₂CH₃,CH₂-cyclopropyl, CHF-cyclopropyl, CH(OH)-cyclopropyl, CH₂OCH₂Ph,CH₂(4-F-Ph), CH₂(4-CF₃-Ph), CH₂-[1,2,4]triazol-4-yl,CH₂-(imidazol-1-yl), CH₂-(pyrazol-1-yl), CH₂—COOCH₂Ph, CH₂—COOH,CH₂—CONMe2, and CH₂OCH₃.
 21. The compound of claim 20 wherein R⁹ and R¹⁰are each independently hydrogen or methyl.
 22. The compound of claim 4which is selected from the group consisting of:

or a pharmaceutically acceptable salt thereof.
 23. The compound of claim4 of the structural formula selected from the group consisting of:

R³ R⁸ R¹ 2-F,5-F H CF₃ 2-F,4-F,5-F CH₂(4-CF₃—Ph) CF₃ 2-F,4-F,5-FCH₂(4-F—Ph) CF₃ 3-F,4-F CH₂(4-F—Ph) CF₃ 3-F,4-F CHOH(cPr) CF₃2-F,4-F,5-F H CF₃ 2-F,4-F,5-F CH₂OCH₂Ph CF₃ 3-F,4-F CH₂(1,2,4- CF₃triazol-1-yl) 2-F,4-F,5-F CH₂(imidazol-1- CF₃ yl) 2-F,4-F,5-FCH₂(pyrazol-1- CF₃ yl) 2-F,5-F Me CF₃ 2-F,4-F,5-F CH₂CO₂CH₂Ph CF₃2-F,4-F,5-F H CHF₂ 2-F,4-F,5-F Me CHF₂ 2-F,4-F,5-F CH₂OMe CF₃.


24. A pharmaceutical composition which comprises a compound of claim 1and a pharmaceutically acceptable carrier.
 25. (canceled)
 26. (canceled)27. A method for treating or controlling non-insulin dependent (Type 2)diabetes in a mammal in need thereof which comprises the administrationto the mammal of a therapeutically effective amount of a compound ofclaim
 1. 28-31. (canceled)
 32. The pharmaceutical composition of claim24 further comprising one or more additional active ingredients selectedfrom the group consisting of: (a) a second dipeptidyl peptidase IVinhibitor; (b) an insulin sensitizer selected from the group consistingof a PPARγ agonist, a PPARα/γ dual agonist, a PPARα agonist, abiguanide, and a protein tyrosine phosphatase-1B inhibitor; (c) aninsulin or insulin mimetic; (d) a sulfonylurea or other insulinsecretagogue; (e) an α-glucosidase inhibitor; (f) a glucagon receptorantagonist; (g) GLP-1, a GLP-1 mimetic, or a GLP-1 receptor agonist; (h)GIP, a GIP mimetic, or a GIP receptor agonist; (i) PACAP, a PACAPmimetic, or a PACAP receptor agonist; (j) a cholesterol lowering agentsuch as (i) HMG-CoA reductase inhibitor, (ii) sequestrant, (iii)nicotinyl alcohol, nicotinic acid or a salt thereof, (iv) PPARα agonist,(v) PPARα/γ dual agonist, (vi) inhibitor of cholesterol absorption,(vii) acyl CoA:cholesterol acyltransferase inhibitor, and (viii)anti-oxidant; (k) a PPARδ agonist; (l) an antiobesity compound; (m) anileal bile acid transporter inhibitor; and (n) an anti-inflammatoryagent. 33-34. (canceled)